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Yoon, Sang Hoon Kim Dong Joo. "Growth and characterization of ZNO and PZT films for micromachined acoustic wave devices." Auburn, Ala, 2009. http://hdl.handle.net/10415/1719.
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Olzick, Adam. "Deposition, Characterization, and Fabrication of a Zinc Oxide Piezoelectric Thin Film Microspeaker Using DC Reactive Sputtering." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/767.
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A piezoelectric microspeaker device that could be used in a variety of acoustic applications was designed and fabricated using a thin film ZnO layer that was reactively DC sputtered onto a single crystalline n-type silicon substrate. When tested the microspeaker did not produce sound due to complications in the etching process, the thickness of the diaphragms, and clamping effects. Instead, a characterization approach was taken and the structural, optical, electrical, and piezoelectric properties of the ZnO were investigated. Scanning electron microscopy, x-ray diffraction, and atomic force microscopy were utilized to discover the ZnO’s structural properties. Using the XRD and SEM, the as-sputtered ZnO films were found to have highly c-axis oriented columnar crystals. Optical properties were determined from the reflectance spectrums obtained from a Filmetrics F20 reflectometer and were used to determine the film thickness, the optical constants, and the optical band gap of the ZnO thin films. Using a four-point probe, the as-sputtered ZnO films were found to be highly resistive and insulative, mainly due to voided growth boundaries between the crystals. To improve electrical conductivity and piezoelectric response, ZnO samples were annealed at varying temperatures in a nitrogen environment. The annealing process successfully increased the electrical conductivity and piezoelectric properties of the films. The local piezoelectric properties of the ZnO were discovered with an Asylum MFP-3D and a piezoresponse force microscopy (PFM) technique called DART-PFM. The ZnO films that were sputtered with 70 watts and an argon to oxygen gas ratio of 2:1 were found to have the highest d33 piezoelectric coefficients. The ZnO sample that was annealed at 600°C for 30 minutes had the highest overall d33 value of 4.0 pm/V, which means that the 600°C annealed ZnO films would have the best chance of making a functional microspeaker.
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Iqbal, Abid. "The Sputtering and Characterization of C-Axis Oriented Aluminium Nitride Thin Films On Top Of Cubic Silicon Carbide-On-Silicon Substrates for Piezoelectric Applications." Thesis, Griffith University, 2017. http://hdl.handle.net/10072/365840.
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The growth of micro-scale wireless electronics is increasing significantly because of their miniaturisation and low power consumption. These devices currently draw power from batteries or chemical fuel cells. Their limited life-spans prompt active research to find an alternative solution by harvesting ambient energy from the environment. Numerous sources are available such as solar, thermoelectric, acoustic, and mechanical vibrations. Among them, mechanical vibration is perhaps the most practical to power these wireless electronic devices via piezoelectric transduction. Three most common piezoelectric materials are Lead zirconate titanate (PZT), zinc oxide (ZnO) and aluminum nitride (AlN). AlN is preferred over ZnO and PZT for several reasons. Chiefly among them is because it has the highest electromechanical coupling along the c-axis of wurzite AlN for longitudinal deformation. This thesis investigates the sputtering of c-axis oriented AlN on top of cubic-silicon carbide-on-silicon (3C-SiC-on-Si) substrates for piezoelectric applications. The 3C-SiC buffer layer was used to reduce the lattice mismatch and thermal expansion coefficient between AlN and Si. In the first part of the research, RF sputtering was utilised for depositing AlN. The low growth rate of RF sputtering prompted the switch to DC sputtering. The DC sputtering suffered from electrical arching problems, which were addressed by gradually decreasing the sputtering pressure. However, the system had the limitation of 1200 W of maximum power.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
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Chawich, Juliana. "ZnO/GaAs-based acoustic waves microsensor for the detection of bacteria in complex liquid media." Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCD012/document.
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Cette thèse s’inscrit dans le cadre d’une cotutelle internationale entre l’Université de Bourgogne Franche-Comté en France et l’Université de Sherbrooke au Canada. Elle porte sur le développement d'un biocapteur miniature pour la détection et la quantification de bactéries dans des milieux liquides complexes. La bactérie visée est l’Escherichia coli (E. coli), régulièrement mise en cause dans des épidémies d'infections alimentaires, et parfois meurtrière.La géométrie du biocapteur consiste en une membrane en arséniure de gallium (GaAs) sur laquelle est déposé un film mince piézoélectrique d’oxyde de zinc (ZnO). L'apport du ZnO structuré en couche mince constitue un réel atout pour atteindre de meilleures performances du transducteur piézoélectrique et consécutivement une meilleure sensibilité de détection. Une paire d'électrodes déposée sur le film de ZnO permet de générer sous une tension sinusoïdale une onde acoustique se propageant dans le GaAs, à une fréquence donnée. La face arrière de la membrane, quant à elle, est fonctionnalisée avec une monocouche auto-assemblée (SAM) d'alkanethiols et des anticorps anti-E. coli, conférant la spécificité de la détection. Ainsi, le biocapteur bénéficie à la fois des technologies de microfabrication et de bio-fonctionnalisation du GaAs, déjà validées au sein de l’équipe de recherche, et des propriétés piézoélectriques prometteuses du ZnO, afin d’atteindre potentiellement une détection hautement sensible et spécifique de la bactérie d’intérêt. Le défi consiste à pouvoir détecter et quantifier cette bactérie à de très faibles concentrations dans un échantillon liquide et/ou biologique complexe.Les travaux de recherche ont en partie porté sur les dépôts et caractérisations de couches minces piézoélectriques de ZnO sur des substrats de GaAs. L’effet de l’orientation cristalline du GaAs ainsi que l’utilisation d’une couche intermédiaire de Platine entre le ZnO et le GaAs ont été étudiés par différentes techniques de caractérisation structurale (diffraction des rayons X, spectroscopie Raman, spectrométrie de masse à ionisation secondaire), topographique (microscopie à force atomique), optique (ellipsométrie) et électrique. Après la réalisation des contacts électriques, la membrane en GaAs a été usinée par gravure humide. Une fois fabriqué, le transducteur a été testé en air et en milieu liquide par des mesures électriques, afin de déterminer les fréquences de résonance pour les modes de cisaillement d’épaisseur. Un protocole de bio-fonctionnalisation de surface, validé au sein du laboratoire, a été appliqué à la face arrière du biocapteur pour l’ancrage des SAMs et des anticorps, tout en protégeant la face avant. De plus, les conditions de greffage d’anticorps en termes de concentration utilisée, pH et durée d’incubation, ont été étudiées, afin d’optimiser la capture de bactérie. Par ailleurs, l’impact du pH et de la conductivité de l’échantillon à tester sur la réponse du biocapteur a été déterminé. Les performances du biocapteur ont été évaluées par des tests de détection de la bactérie cible, E. coli, tout en corrélant les mesures électriques avec celles de fluorescence. Des tests de détection ont été réalisés en variant la concentration d’E. coli dans des milieux de complexité croissante. Différents types de contrôles ont été réalisés pour valider les critères de spécificité. En raison de sa petite taille, de son faible coût de fabrication et de sa réponse rapide, le biocapteur proposé pourrait être potentiellement utilisé dans les laboratoires de diagnostic clinique pour la détection d’E. coliThis thesis was conducted in the frame of an international collaboration between Université de Bourgogne Franche-Comté in France and Université de Sherbrooke in Canada. It addresses the development of a miniaturized biosensor for the detection and quantification of bacteria in complex liquid media. The targeted bacteria is Escherichia coli (E. coli), regularly implicated in outbreaks of foodborne infections, and sometimes fatal.The adopted geometry of the biosensor consists of a gallium arsenide (GaAs) membrane with a thin layer of piezoelectric zinc oxide (ZnO) on its front side. The contribution of ZnO structured in a thin film is a real asset to achieve better performances of the piezoelectric transducer and consecutively a better sensitivity of detection. A pair of electrodes deposited on the ZnO film allows the generation of an acoustic wave propagating in GaAs under a sinusoidal voltage, at a given frequency. The backside of the membrane is functionalized with a self-assembled monolayer (SAM) of alkanethiols and antibodies anti-E. coli, providing the specificity of detection. Thus, the biosensor benefits from the microfabrication and bio-functionalization technologies of GaAs, validated within the research team, and the promising piezoelectric properties of ZnO, to potentially achieve a highly sensitive and specific detection of the bacteria of interest. The challenge is to be able to detect and quantify these bacteria at very low concentrations in a complex liquid and/or biological sample.The research work partly focused on the deposition and characterization of piezoelectric ZnO thin films on GaAs substrates. The effect of the crystalline orientation of GaAs and the use of a titanium / platinum buffer layer between ZnO and GaAs were studied using different structural (X-ray diffraction, Raman spectroscopy, secondary ionization mass spectrometry), topographic (atomic force microscopy), optical (ellipsometry) and electrical characterizations. After the realization of the electrical contacts on top of the ZnO film, the GaAs membrane was micromachined using chemical wet etching. Once fabricated, the transducer was tested in air and liquid medium by electrical measurements, in order to determine the resonance frequencies for thickness shear mode. A protocol for surface bio-functionalization, validated in the laboratory, was applied to the back of the biosensor for anchoring SAMs and antibodies, while protecting the top side. Furthermore, different conditions of antibody grafting such as the concentration, pH and incubation time, were tested to optimize the immunocapture of bacteria. In addition, the impact of the pH and the conductivity of the solution to be tested on the response of the biosensor has been determined. The performances of the biosensor were evaluated by detection tests of the targeted bacteria, E. coli, while correlating electrical measurements with fluorescence microscopy. Detection tests were completed by varying the concentration of E. coli in environments of increasing complexity. Various types of controls were performed to validate the specificity criteria. Thanks to its small size, low cost of fabrication and rapid response, the proposed biosensor has the potential of being applied in clinical diagnostic laboratories for the detection of E. coli
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Yang, Zheng. "Doping in zinc oxide thin films." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3359913.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 12, 2010). Includes bibliographical references. Also issued in print.
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Depaz, Michael. "Processing and characterization of zinc oxide thin films." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002235.
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Yang, Hung-Pao 1980. "A study of P-type zinc oxide thin films /." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99550.
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In the past decade, p-type ZnO material has been investigated extensively. Its properties offer the potential for broad applications including the development of ultraviolet light emitting devices. Although n-type ZnO material is well known and studied for decades, the fabrication method and properties of p-type ZnO material are still to date not clearly understood.In this report, reproducible p-type ZnO thin films sputtered on glass substrates are reported. On the same substrate, p-type ZnO film is local and surrounded by n-type ZnO regions. The thickness of the films is typically three microns after several hours of deposition by radio-frequency magnetron sputtering technique. Both p-type ZnO and n-type thin films are characterized by optical and electrical measurements at room temperature.
The crystal structure of p-type ZnO is examined by X-ray diffraction patterns. The X-ray diffraction patterns show that the material is polycrystalline and has (100) and (101) preferred orientation. Photoluminescence spectra of ZnO help to identify the energy levels in the material and spectra analysis reveals the presence of defects and dopants in the material. For p-type ZnO, the resistivity, the hole concentration and hole mobility are found to be 148.8 O-cm, 4.34 x 1018/cm3 and 1.72 x 10-2 cm2/V-sec respectively.
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Potter, D. "Zinc-based thin films for transparent conducting oxide applications." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10041886/.
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This thesis describes the synthesis of zinc-based transparent conducting oxide (TCO) thin films, as sustainable alternatives to commercial TCOs. There are two main aims to this work. The first is the discovery of suitable TCO materials, which involves finding the optimum optoelectronic properties for applications in photovoltaic devices. The second aim is investigating the scale up of aerosol assisted chemical vapour deposition (AACVD), which is the technique used to deposit the majority of the films in this work. The films deposited in this work were characterised by X-ray diffraction (XRD) to find the crystal structures, X-ray photoelectron spectroscopy (XPS) to find the elemental compositions, scanning electron microscopy (SEM) to analyse the surface morphologies, UV/vis spectroscopy to find the optical properties, and by Hall effect measurements to find the electrical properties. Aluminium, gallium, indium, silicon, and fluorine have been examined as dopants for ZnO, in various combinations, and at different concentrations. The films were generally found to have high transparency, and electrical properties that approached those of industrial TCO materials. The merits of the films are particularly promising, when considering the relative ease through which the films were synthesised. Additionally, the effect of varying the solvent used to make up the precursor solution is investigated. The deposition of ZnSb2O6 thin films via spin coating is also discussed. This thesis also details an investigation into the scale-up of AACVD. An aerosol transport study was performed, whereby the aerosol was transported prior to deposition. It was found that a considerable amount of aerosol was condensing within the tubing, prior to reaching the reactor. Additionally, increasing the film growth rates was investigated by depositing FTO films using high concentrations in the precursor solution. Growth rates of approximately 2 μm min-1 were achieved, making the use of AACVD for commercial applications significantly more feasible.
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Min, Yongki 1965. "Properties and sensor performance of zinc oxide thin films." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17032.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.Includes bibliographical references (p. 144-152).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Reactively sputtered ZnO thin film gas sensors were fabricated onto Si wafers. The atmosphere dependent electrical response of the ZnO micro arrays was examined. The effects of processing conditions on the properties and sensor performance of ZnO films were investigated. Using AFM, SEM, XRD and WDS, the 02/Ar ratios during sputtering and Al dopant were found to control the property of ZnO films. Subsequent annealing at 700 C improved the sensor response of the films considerably although it had only minor effects on the microstructure. DC resistance, I-V curves and AC impedance were utilized to investigate the gas response of ZnO sensors. ZnO films prepared with high O2/Ar ratios showed better sensitivity to various gases, a feature believed to be related to their lower carrier density. Al doped ZnO showed measurable sensitivity even with lower resistance attributable to their porous microstructure. AC impedance identified two major components of the total resistance including Schottky barriers at the Pt-ZnO interfaces and a DC bias induced constriction resistance within the ZnO films. Time dependent drift in resistance of ZnO films has been observed. Without applied bias, the ZnO films showed a fast and a slow resistance change response when exposed to gases with varying oxygen partial pressure with both response components dependent on operating temperature. Even at the relatively low operating temperatures of these thin film sensors, bulk diffusion cannot be discounted. The oxygen partial pressure dependence of the sensor resistance and its corresponding activation energy were related to defect process controlling the reduction/oxidation behavior of the ZnO.
(cont.) In this study, time dependent DC bias effects on resistance drift were first discovered and characterized. The DC bias creates particularly high electric fields in these micro devices given that the spacing of the interdigited electrodes falls in the range of microns. The high electric field is believed to initiate ion migration and/or modulate grain boundary barrier heights, inducing resistance drift with time. Such DC bias resistance induced drift is expected to contribute to the instability of thin film micro array sensors designed for practical applications. Suggestions for stabilizing sensor response are provided.
by Yongki Min.
Ph.D.
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Choppali, Uma. "Low Temperature Polymeric Precursor Derived Zinc Oxide Thin Films." Thesis, University of North Texas, 2006. https://digital.library.unt.edu/ark:/67531/metadc5504/.
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Zinc oxide (ZnO) is a versatile environmentally benign II-VI direct wide band gap semiconductor with several technologically plausible applications such as transparent conducting oxide in flat panel and flexible displays. Hence, ZnO thin films have to be processed below the glass transition temperatures of polymeric substrates used in flexible displays. ZnO thin films were synthesized via aqueous polymeric precursor process by different metallic salt routes using ethylene glycol, glycerol, citric acid, and ethylene diamine tetraacetic acid (EDTA) as chelating agents. ZnO thin films, derived from ethylene glycol based polymeric precursor, exhibit flower-like morphology whereas thin films derived of other precursors illustrate crack free nanocrystalline films. ZnO thin films on sapphire substrates show an increase in preferential orientation along the (002) plane with increase in annealing temperature. The polymeric precursors have also been used in fabricating maskless patterned ZnO thin films in a single step using the commercial Maskless Mesoscale Materials Deposition system.
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Huang, Bin. "Mechanical characterization of thin films /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20HUANG.
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Li, Sonny X. "Nitrogen doped zinc oxide thin film." Berkeley, Calif. : Oak Ridge, Tenn. : Lawrence Berkeley National Laboratory ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/821916-VLVAK9/native/.
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Thesis (M.S.); Submitted to the University of California, Berkeley, 210 Hearst Mining Memorial Bldg., Berkeley, CA 94720 (US); 15 Dec 2003.Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--54116" Li, Sonny X. USDOE Director. Office of Science. Basic Energy Sciences (US) 12/15/2003. Report is also available in paper and microfiche from NTIS.
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Miller, Paul. "Zinc Oxide: A spectroscopic investigation of bulk crystals and thin films." Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/3618.
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The optical properties of zinc oxide crystals and thin films prepared by different methods are investigated. Single crystal zinc oxide samples prepared by melt and hydrothermal growth techniques were obtained. The influence of polarity and growth method on the optical properties were studied and correlated with their electronic properties. Thin films prepared by molecular beam epitaxy (MBE) and sputtering were studied and the influence of growth conditions and post growth treatment on the optical properties of the films was investigated. The photo-luminescence (PL) of bulk zinc oxide was examined at high resolution. Line widths of less than 0.1 meV were observed. More than a dozen different transitions in the near band edge region (NBE 360-380 nm) were noted, several of which displayed a separation of <0.5 meV which goes some way to illustrating the complexity of the system. Attempts were made, with some success, to reconcile the two main competing identification systems of the NBE transitions and explanations for some of the discrepancies are provided. The controversial deep level transitions in the visible part of the spectrum are fit with 3 Gaussians and their identities discussed with relation to the available literature. The presence of copper impurities was detected in annealed films and a model to explain their behaviour under annealing conditions is hypothesised. Films grown by MBE here at the University of Canterbury are shown to have PL line widths of as little as 2.2 meV, the ratio of active oxygen species in the growth chamber during deposition is shown to effect the optical quality of the films. It is shown that annealing can improve the optical quality of the films and various other methods of influencing the films properties are discussed. Reactive, magnetron, direct current sputtering is shown to be the optimal method of growth for maximising both optical and piezo-electric properties. Optimum annealing temperatures were found at 900 and 1100 ℃ with a local minimum at 1000 ℃. X-ray diffraction, atomic force and scanning electron microscopy measurements in addition to optical PL measurements show the influence of annealing on the polycrystalline sputtered ZnO films. Films grown on glass, silicon, sapphire and quartz were shown to display similar behaviour under annealing conditions. It was found that zinc oxide based devices were liable to be chemically unstable at temperatures above 1100 ℃. The piezo electric properties of the films were examined and attempts were made to prepare a zinc oxide film optimised for both optical quality and piezoelectric properties for possible future applications of a hybrid opto-mechanical coupled devices.
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Zhang, Rong. "Zinc Oxide Thin Films for Dye-Sensitized Solar Cell Applications." Miami University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=miami1186016777.
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Ali, Arshid Mahmood. "Characterisation of semi-conductor zinc oxide (ZnO) thin films as photocatalysts." Thesis, University of Auckland, 2011. http://hdl.handle.net/2292/7203.
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The objective of this project was to study the suitability of nanostructured ZnO thin films as efficient photocatalysts and to characterise any issues that may be involved in the scale-up of photocatalytic systems based on these types of immobilised nanostructure ZnO thin films. In particular, this study involved fabricating and then evaluating the effectiveness of a range of nanostructured zinc oxide (ZnO) thin films with different structures and chemistries (i.e. undoped and doped) as photocatalysts, and thereafter to systematically relate: the initial and reacted surface morphology; photocatalytic activity in terms of reaction rate; reaction intermediates and products; and liquid phase and solid phase reaction mechanisms under both limited and rich oxygen conditions at two different UV irradiation wavelengths (254nm and 340nm). These nanostructured thin films (i.e. undoped ZnO; nitrogen doped ZnO - N:ZnO; cobalt doped ZnO - Co:ZnO) were produced using an innovative combination of magnetron sputtered surfaces and hydrothermal solution deposition that allows the morphology, porosity and thickness to be controlled by varying the composition and processing conditions. SEM, UV-Vis, HPLC, LC-MS, AAS and XRD were used to study the changes in thin film morphology, Methylene Blue (MB) degradation and its reaction intermediates, the presence of Zn metal in the reaction fluid, if any, and crystallinity before and after the photocatalytic reaction respectively. Undoped ZnO thin films: Results showed a clear relationship between surface morphology (and the related thin film preparation method) and photocatalytic activity for the ZnO thin film supported catalysts: the tallest, most aligned structure had the highest photocatalytic activity, whilst the smallest, least aligned structure had the lowest. Thus, the MB degradation rate was the fastest for the ZnO thin film (S2-MS) with a uniform arrayed structure. Adding oxygen made the films more stable: in oxygen-limited conditions, SEM and atomic absorption spectroscopy indicated zinc leaching had occurred. Furthermore, with additional oxygen the zinc leaching was minimised under the same reaction conditions. It is thought that this additional oxygen is either minimising the release of, or replacing lost ZnO lattice oxygens, indicating that this ZnO photocatalytic oxidation could be occurring via a Mars van Krevelen type redox mechanism. There was also a significant difference in MB degradation rates, as well as reaction intermediate formation and destruction rates, correlated to the morphologies and crystallinity at both UV wavelengths, with the highest reaction rates at 340nm. Reaction analysis indicates that there is a competition between two different photocatalytic mechanisms: conventional photocatalysed radical oxidation and lattice oxygen-driven oxidation. The dominant reaction mechanism depends on the thin film morphology, crystallinity, availability of oxidant and the wavelength of the incident UV. The surface-photocatalysed radical formation was predominant for more aligned, highly crystalline, morphologies, where there was plentiful oxygen and UV irradiation at 340nm. Lattice oxygen photodegradation was predominant for the less aligned, more amorphous morphologies and UV irradiation at 254nm. Doped (Co:ZnO) thin films: Results showed that cobalt dopant increases the photo-stability of the corresponding undoped thin films under oxygen-limited conditions - increasing with the increased dopant concentration. This increased stability of Co:ZnO nanostructure thin films comes with a price, however: the photocatalytic activity and concomitant degradation of MB and its azo dyes reaction intermediates is in general lowered, compared to the undoped ZnO thin films. At higher dopant concentrations, under oxygen-rich conditions and with UV irradiation at 254nm and 340nm, the MB degradation most likely occurs via a conventional photocatalytic reaction mechanism and/or via charge transfer of the MB into Azure B (AB) with the absence of Mars van Krevelen type mechanism (because of the increased lattice stability). At lower dopant concentrations under oxygen-limited conditions with UV irradiation at 254nm and 340nm, the Mars van Krevelen type reaction mechanism is probably the main mechanism propagating the oxidation of MB. Overall, the undoped morphologies were more photocatalytically active compared to the doped morphologies. In general, this work has shown that several different solid and liquid phase photocatalytic reaction mechanisms govern the photocatalytic degradation of azo dyes such as MB on nanostructured ZnO thin films, and that surface morphology, crystallinity, lack or presence of oxygen, and the dopant concentration are the key parameters governing the overall photocatalytic activity and the activation of these different solid and liquid photocatalytic reaction mechanisms.
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Weigand, Christian Carl. "Zinc Oxide Nanostructures and Thin Films Grown by Pulsed Laser Deposition." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18268.
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ZnO nanostructures have received great attention during the past decade due to numerous potential applications. In order to enable the fabrication of functional devices, reproducible preparation of such nanostructures is necessary. Therefore, a good understanding of the fundamental processes involved in the formation of ZnO nanostructures is indispensable for improving the controllability of nanostructure growth. This work elucidates various aspects of the essential nucleation and growth mechanisms at work during the growth of ZnO nanostructures by catalyst-assisted pulsed laser deposition (PLD). ZnO nanowires and triangular nanosheets have been grown on sapphire substrates by Auassisted PLD. In a first study, the influence of thermal substrate pretreatments on the size and density of the ZnO nanostructures is investigated. It has been found that the presence of surface nucleation sites can compete with nucleation at the Au catalyst and lead to reduced nanostructure sizes and densities. Furthermore, it has been observed that the ZnO morphology switches from nanowires to triangular nanosheets upon increasing oxygen partial pressure in the growth chamber. Electron microscopy results indicates that the catalyst-nanowire growth interface plays an important role in this morphology change. Formation mechanisms of the two different nanostructure types are presented and possible links between oxygen pressure and morphology via growth kinetics and supersaturation considerations are discussed. Additionally, the epitaxial relationships between the two ZnO nanostructure types and sapphire substrates have been investigated in detail by combining x-ray pole figure measurements with both transmission and scanning electron microscope observations. ZnO nanowires growing tilted on c-plane sapphire showed an epitaxial alignment with a buried and inclined substrate plane. Two degenerate configurations have been identified for these tilted wires, promoted by equally low lattice mismatches. On a-plane sapphire, ZnO nanosheets and -wires show distinct differences in the epitaxial relationships with the substrate, indicating a direct correlation to the morphology. The findings about ZnO nanostructures presented in this thesis help to improve control over catalyst-assisted nanostructure growth techniques and provide a further step towards reproducible nanostructure fabrication. In a second part of the thesis, the electrical and optical properties of Al-doped ZnO (AZO) thin films grown on GaAs substrates by PLD have been investigated. AZO is a promising candidate for substituting indium tin oxide as transparent electrodes in optoelectronic applications. The aim of the study is to assess the suitability of AZO as a transparent electrode shell around GaAs nanowire solar cells for direct charge carrier pathways. Furthermore, the portability of previously reported results obtained on transparent substrates such as glass or sapphire to the opaque GaAs substrate is discussed.
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Wellenius, Patrick. "Nitrogen Doping and Ion Beam Processing of Zinc Oxide Thin Films." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-01042006-015801/.
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The modification of single crystal epitaxial ZnO thin films grown by Pulsed Laser Deposition on c-axis oriented sapphire substrates by Ion Beam Processing was investigated. Nitrogen doping of the films was attempted using nuclear transmutation using the 16O (3He, 4He) 15O reaction at 6.6 MeV. The 15O product is unstable and decays to 15N after several minutes by positron emission. There are several potential advantages to using nuclear transmutation including producing nitrogen atoms on the correct lattice site for doping and reduced crystal damage as compared to conventional ion beam implantation. In the experiments in this thesis the doping levels achieved ~1014 cm-3 were too low to be expected to dope the films to p-type. However several beneficial effects due to the ion beam processing were observed, including large increases in resistivity, reduction of defect luminescence, and substantial increases in the response of photoconductive detectors. In addition to desired effects in some films it was also found that in some films bubble like structures approximately 10 ìm in diameter were formed where the thin film delaminated from the surface. It was assumed that mechanism for the bubble formation was the build up of helium gas at the sapphire/ZnO interface.
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Shantheyanda, Bojanna P. "Characterization of aluminum doped zinc oxide thin films for photovoltaic applications." Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4538.
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Growing demand for clean source of energy in the recent years has increased the manufacture of solar cells for converting sun energy directly into electricity. Research has been carried out around the world to make a cheaper and more efficient solar cell technology by employing new architectural designs and developing new materials to serve as light absorbers and charge carriers. Aluminum doped Zinc Oxide thin film, a Transparent conductive Oxides (TCO) is used as a window material in the solar cell these days. Its increased stability in the reduced ambient, less expensive and more abundance make it popular among the other TCO's. It is the aim of this work to obtain a significantly low resistive ZnO:Al thin film with good transparency. Detailed electrical and materials studies is carried out on the film in order to expand knowledge and understanding. RF magnetron sputtering has been carried out at various substrate temperatures using argon, oxygen and hydrogen gases with various ratios to deposit this polycrystalline films on thermally grown SiO[sub]2 and glass wafer. The composition of the films has been determined by X-ray Photoelectron Spectroscopy and the identification of phases present have been made using X-ray diffraction experiment. Surface imaging of the film and roughness calculations are carried out using Scanning Electron Microscopy and Atomic Force Microscopy respectively. Determination of resistivity using 4-Probe technique and transparency using UV spectrophotometer were carried out as a part of electrical and optical characterization on the obtained thin film. The deposited thin films were later annealed in vacuum at various high temperatures and the change in material and electrical properties were analyzed.ID: 028916634; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.)--University of Central Florida, 2010.; Includes bibliographical references (p. 74-76).
M.S.
Masters
School of Electrical Engineering and Computer Science
Engineering and Computer Science
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Herodotou, Stephania. "Zirconium doped zinc oxide thin films deposited by atomic layer deposition." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2013045/.
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Doped zinc oxide is of interest as a transparent conductive oxide (TCO), due to the abundance of its major constituents, its low resistivity, high transparency and wide bandgap. The current work focuses on the properties required for TCO applications including resistivity of ≤10-3 Ω•cm, carrier density of ≥1020 cm-3, and transparency >80% in the visible light. Zirconium (Zr4+) was chosen as the dopant in the current work due to its abundance, comparable ionic size to Zn and because it can act as a double donor providing up to two extra free electrons per ion when substituted for Zn2+. The doping process can be controlled using atomic layer deposition (ALD), with the doped films resulting in an increased conductivity. The films in the current work resulted in a minimum resistivity of 1.44×10-3 Ω•cm and maximum carrier density of 3.81×1020 cm-3 for films <100 nm thickness, having 4.8 at.% Zr concentration. The resistivity was further reduced after reducing the interfacial and grain boundary scattering (i.e. increase grain size), by increasing the overall film thickness. The resistivity of 7.5×10-4 Ω•cm, carrier mobility of 19.6 cm2V‒1s-1 and carrier density of 4.2×1020 cm-3 were measured for a 250 nm thick film with 4.8 at.% doping. The tuning of the carrier density via doping offers control over the optical gap due to the net effect of Burstein-Moss effect and bandgap renormalisation. This resulted to an increase of the optical gap from 3.2 eV for the un-doped ZnO to 3.5 eV for 4.8 at.% Zr-doped films. The average optical transparency in the visible/near IR range was as high as 91% for 4.8 at.% doped films. The thickness increase also resulted in a grain orientation shift from perpendicular to the substrate (i.e. polar c-plane orientation) to parallel (i.e. non-polar m-plane) due to the strain increase that forced the films to grow at a low strain energy direction. This offers the possibility of growing non-polarised films that show no piezoelectric field charge observed in polar oriented films. Therefore, controlling the grain size through the number of ALD cycles can effectively result in mobility and preferred orientation control, while the doping concentration controls the resistivity, optical bandgap and transparency of the films.
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Franklin, Joseph B. "Pulsed laser deposition of zinc oxide thin films for optoelectronic applications." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10115.
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Zinc oxide (ZnO) thin films have great promise for a wide range of optoelectronic applications, however controlling crystallinity and stoichiometry at low processing temperatures remains a challenge. Pulsed laser deposition (PLD) is a versatile technique that allows precise control the film properties. The crystallinity and electrical properties can, theoretically, be tuned by altering a wide variety of deposition parameters. However, until now there has been little work performed exploring PLD as a technique for the preparation of thin films at low temperature, for use in optoelectronic applications. In this thesis, PLD is demonstrated as a highly appropriate technique for the preparation of semiconducting and electrically conducting transparent films, over a wide range of substrate temperatures applicable for optoelectronic grade substrates. Deposition conditions are identified allowing the low temperature deposition of ZnO directly onto functional organic poly(3-hexylthiophene) (P3HT) coated substrates. To demonstrate the applicability of this methodology the preparation of conventional architecture hybrid (inorganic:organic) photovoltaic devices is outlined with no degradation to the microstructure, optical or electrical properties of the P3HT observed. The methodology is widely applicable for depositing oxide interlayers multilayer organic devices. In this thesis, the role of ZnO is investigated as i) an exciton dissociation and electron transporting layer in hybrid devices, ii) an optical spacing layer in organic bulk heterojunction photovoltaic devices and iii) as a transparent conducting oxide (when doped with A1) as a top contact for organic optoelectronic devices. Device performance is optimised through careful control of PLD parameters. In each device and in free-standing thin films the microstructure, morphology and crystallographic nature of the as-deposited ZnO is studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The electrical properties are studied in both operational devices and by 4-point probe measurements.
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Hlaing, Oo Win Maw. "Infrared spectroscopy of zinc oxide and magnesium nanostructures." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/w_hlaingoo_121107.pdf.
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Mahmood, Farkhund Shakeel. "Electrical and optical properties of RF sputtered ZnO thin films." Thesis, Keele University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297202.
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Yin, Shi. "Integration of epitaxial piezoelectric thin films on silicon." Thesis, Ecully, Ecole centrale de Lyon, 2013. http://www.theses.fr/2013ECDL0039/document.
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Les matériaux piézoélectriques, comme le titanate-zirconate de plomb Pb(ZrxTi1-x)O3 (PZT), l’oxyde de zinc ZnO, ainsi que la solution solide de Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), sont actuellement l’objet d’études de plus en plus nombreuses à cause de leurs applications innovantes dans les systèmes micro-électromécaniques (MEMS). Afin de les intégrer sur substrat de silicium, certaines précautions doivent être prises en compte concernant par exemple des couches tampon, les électrodes inférieures. Dans cette thèse, des films piézoélectriques (PZT et PMN-PT) ont été épitaxiés avec succès sous forme de monocristaux sur silicium et SOI (silicon-on-insulator) par procédé sol-gel. En effet, des études récentes ont montré que les films piézoélectriques monocristallins semblent posséder des propriétés supérieures à celles des films polycristallins, permettant ainsi une augmentation de la performance des dispositifs MEMS. Le premier objectif de cette thèse était de réaliser l'épitaxie de film monocristallin de matériaux piézoélectriques sur silicium. L'utilisation d’une couche tampon d'oxyde de gadolinium (Gd2O3) ou de titanate de strontium (SrTiO3 ou STO) déposés par la technique d’épitaxie par jets moléculaires (EJM) a été explorée en détail pour favoriser l’épitaxie du PZT et PMN-PT sur silicium. Sur le système Gd2O3/Si(111), l’étude par diffraction des rayons X (XRD) de la croissance du film PZT montre que le film est polyphasé avec la présence de la phase parasite pyrochlore non ferroélectrique. Cependant, le film PZT déposé sur le système STO/Si(001) est parfaitement épitaxié sous forme d’un film monocristallin. Afin de mesurer ses propriétés électriques, une couche de ruthenate de strontium conducteur SrRuO3 (SRO) déposée par ablation laser pulsé (PLD) a été utilisée comme l'électrode inférieure à cause de son excellente conductibilité et de sa structure cristalline pérovskite similaire à celle du PZT. Les caractérisations électriques sur des condensateurs Ru/PZT/SRO démontrent de très bonnes propriétés ferroélectriques avec présence de cycles d'hystérésis. Par ailleurs, le matériau relaxeur PMN-PT a aussi été épitaxié sur STO/Si comme l’a confirmé la diffraction des rayons X ainsi que la microscopie électronique en transmission (TEM). Ce film monocristallin est de la phase de perovskite sans présence de pyrochlore. En outre, une étude en transmission du rayonnement infrarouge au synchrotron a prouvé une transition de phase diffuse sur une large gamme de température, comme attendue dans le cas d’un relaxeur. L'autre intérêt d'avoir des films PZT monocristallins déposés sur silicium et SOI est de pouvoir utiliser les méthodes de structuration du silicium bien standardisées maintenant pour fabriquer les dispositifs MEMS. La mise au point d’un procédé de micro-structuration en salle blanche a permis de réaliser des cantilevers et des membranes afin de caractériser mécaniquement les couches piézoélectriques. Des déplacements par l'application d'une tension électrique ont ainsi pu être détectés par interférométrie. Finalement, cette caractérisation par interférométrie a été combinée avec une modélisation basée sur la méthode des éléments finis. Dans le futur, il sera nécessaire d’optimiser le procédé de microfabrication du dispositif MEMS afin d’en améliorer les performances électromécaniques. Enfin, des caractérisations au niveau du dispositif MEMS lui-même devront être développées en vue de leur utilisation dans de futures applicationsRecently, piezoelectric materials, like lead titanate zirconate Pb(ZrxTi1-x)O3 (PZT), zinc oxide ZnO, and the solid solution Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), increasingly receive intensive studies because of their innovative applications in the microelectromechanical systems (MEMS). In order to integrate them on silicon substrate, several preliminaries must be taken into considerations, e.g. buffer layer, bottom electrode. In this thesis, piezoelectric films (PZT and PMN-PT) have been successfully epitaxially grown on silicon and SOI (silicon-on-insulator) in the form of single crystal by sol-gel process. In fact, recent studies show that single crystalline films seem to possess the superior properties than that of polycrystalline films, leading to an increase of the performance of MEMS devices. The first objective of this thesis was to realize the epitaxial growth of single crystalline film of piezoelectric materials on silicon. The use of a buffer layer of gadolinium oxide(Gd2O3) or strontium titanate (SrTiO3 or STO) deposited by molecular beam epitaxy (MBE) has been studied in detail to integrate epitaxial PZT and PMN-PT films on silicon. For Gd2O3/Si(111) system, the study of X-ray diffraction (XRD) on the growth of PZT film shows that the film is polycrystalline with coexistence of the nonferroelectric parasite phase, i.e. pyrochlore phase. On the other hand, the PZT film deposited on STO/Si(001) substrate is successfully epitaxially grown in the form of single crystalline film. In order to measure the electrical properties, a layer of strontium ruthenate (SrRuO3 or SRO) deposited by pulsed laser deposition (PLD) has been employed for bottom electrode due to its excellent conductivity and perovskite crystalline structure similar to that of PZT. The electrical characterization on Ru/PZT/SRO capacitors demonstrates good ferroelectric properties with the presence of hysteresis loop. Besides, the relaxor ferroelectric PMN-PT has been also epitaxially grown on STO/Si and confirmed by XRD and transmission electrical microscopy (TEM). This single crystalline film has the perovskite phase without the appearance of pyrochlore. Moreover, the study of infrared transmission using synchrotron radiation has proven a diffused phase transition over a large range of temperature, indicating a typical relaxor ferroelectric material. The other interesting in the single crystalline PZT films deposited on silicon and SOI is to employ them in the application of MEMS devices, where the standard silicon techniques are used. The microfabrication process performed in the cleanroom has permitted to realize cantilevers and membranes in order to mechanically characterize the piezoelectric layers. Mechanical deflection under the application of an electric voltage could be detected by interferometry. Eventually, this characterization by interferometry has been studied using the modeling based on finite element method and analytic method. In the future, it will be necessary to optimize the microfabrication process of MEMS devices based on single crystalline piezoelectric films in order to ameliorate the electromechanical performance. Finally, the characterizations at MEMS device level must be developed for their utilization in the future applications
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Lee, Jim 1963. "Microstructure and properties of zinc oxide nano-crystalline thin films and composites." Thesis, University of Auckland, 2006. http://hdl.handle.net/2292/2136.
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Zinc oxide (ZnO) is a II–VI compound semiconductor with a wide direct band-gap of 3.3 eV and a hexagonal structure. ZnO is often used in the paint, paper, rubber, food and drug industries. It is also a promising material in nanotechnology applications, for example in nano-electronics and nano-robotic technology. With its wide band-gap, high exciton binding energy and high breakdown strength, ZnO can be utilized for electronic and photonic devices, as well as for high-frequency applications. To produce such optoelectronic devices, control of electronic properties, such as the nature of conduction and carrier density, is required. However, such control has proved difficult for ZnO. Much research has been done to pursue p type ZnO using different processing techniques, however, there are few reports addressing the relationships of microstructure on optical and electrical properties, ion implantation doping of ZnO and nano-ZnO polymer composites. The objectives of this project are to study the processing, composition, microstructure, electronic, optical, UV and electromagnetic shielding properties of ZnO thin films and composites; to explore ion implantation as a method to dope Al, Ag, Sb, Sn and TiN into ZnO thin films or single crystals; to develop conducting, transparent oxide films and/or p-type semiconductor for potential device applications; and to study the relationships of doping, microstructure and electro-optical properties of ZnO thin films and nano-ZnO polymer composites. The experimental work included annealing, characterizing and implantation of magnetron sputtering ZnO thins films and ZnO single crystals. Ion implantation was employed to dope ZnO thin films or single crystals with Ti, N, Sb, Al, Sn and Ag. The diffusion behaviour of implanted and annealed ZnO and the ellipsometry of implanted ZnO thin films were investigated. The relationship of microstructure and properties of as-deposited, annealed and implanted ZnO was studied. The results show that compared to direct current (d.c.) sputtering, the films produced using radio frequency (r.f.) have significantly lower resistivity, porosity and stress. The residual stress can change the band gap of ZnO thin films. Conductivity experiments suggest that the conduction mechanism of sputtered ZnO thin films involves charge transport in the conduction band and electronic hopping between the nearest neighbour donor levels. Furthermore, the optical transmission of ZnO thin films is high in the visible, with excellent UV absorption properties. It is also found that annealing alters the grain size and composition, and reduces the stress of ZnO thin films. Moreover, ion implantation causes partial amorphousness of ZnO films in the implantation zone and introduces stress and interstitial dopants. Transport of Ions in Matter (TRIM) modelling and Secondary Ion Mass Spectrometer (SIMS) analysis confirm that lighter elements implant deeper than heavy elements. The implanted ZnO shows some p type tendency and evidence of photoluminescence. Lastly, the nano-ZnO and polymer composites show excellent mechanical, good UV barrier properties.
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Бересток, Таїсія Олександрівна, Таисия Александровна Бересток, Taisiia Oleksandrivna Berestok, Денис Ігорович Курбатов, Денис Игоревич Курбатов, Denys Ihorovych Kurbatov, Володимир Миколайович Кузнєцов, et al. "Structural characteristics of zinc oxide thin films obtained by chemial bath deposition." Thesis, Athens, Greece, 2014. http://essuir.sumdu.edu.ua/handle/123456789/38274.
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Due to the large band gap, high charge-carrier mobility, high exciton binding energy, low toxicity, high thermal and radiation stability, zinc oxide is considered as a promising material for fabrication gas detectors, sensors of ultraviolet light, electroluminescence devices. Furthermore, chemically deposited ZnO films are widely used as conductive and optical cover layers of solar cells. Among the various methods of ZnO thin films obtaining, chemical bath deposition is one of the promising non-vacuum method of synthesis of layers with controllable structural and electrophysical properties.
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Hill, Theresa Y. "Fabrication of Zinc Oxide Thin Films For Renewable Energy and Sensor Applications." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1291251851.
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Morales, Hector Roberto. "Development and integration of thin film zinc oxide integral resistors in SOP." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/19908.
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Rashidi, Nazanin. "Cation and anion doping of ZnO thin films by spray pyrolysis." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:e8261559-8901-409d-8d08-a3fc04b6d734.
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ZnO is an n-type semiconducting material with high optical transparency in the visible range (400 - 750 nm) of the electromagnetic spectrum. When doped with group 13 or 14 metal oxides, ZnO exhibits almost metallic electrical conductivity. ZnO thin films have been recognised as promising alternative material for the currently widely-used but expensive indium oxide in the form of indium tin oxide (ITO), in terms of their low cost and the high abundance of zinc. At the moment, even the best solution-processed ZnO films still can not compete for ITO replacement especially in solar energy utilization and OLED lighting applications, and the performance of ZnO films needs to be further improved. The objective of this work was to enhance the electrical and optical properties of spray pyrolysed ZnO thin films by simultaneous cation and anion doping. This was achieved by growing several series of undoped, single-doped, and co-doped ZnO thin films over a wide range of conditions, in order to understand the growth behaviour of undoped and doped ZnO, and to establish the optimum growth procedure. Spray pyrolysis process has advantages over vacuum-based techniques in terms of its low-cost, high deposition rate, simple procedure and can be applied for the production of large area thin films. Various techniques were employed to characterize the properties of the prepared thin films, and thus determine the optimum growth conditions (i.e. X-ray difiraction (XRD), Xray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-Vis-NIR spectroscopy and Hall effect measurement). The growth of doped ZnO on glass substrates using Si and F as dopants, yielded highly conducting and transparent thin films. The co-doped thin films exhibited distinct widening of band gap upon increasing deposition temperature and doping concentration as a result of increasing electron concentration up to 4.8 x 1020 cm-3 upon doping with Si and F at the same time. The resistivity of the films deposited from Zn(acac)2 · xH2O solutions and at the optimum temperature of 450 °C, was found to decrease from 4.6 x 10-2 Ωcm for the best undoped ZnO film to 3.7 x 10-3 Ωcm, upon doping with 3% Si. The films co-doped with Si and F in the ratios of [Si] / [Zn]= 3 - 4 mol% and [F] / [Zn]=30 - 40 mol% were the most conducting (p ∼ 2.0 x 10-3 Ωcm). The associated optical transmittance of co-doped ZnO was above 85% in the whole visible range. Results compare favourably with In-doped ZnO deposited under similar conditions. Si+F co-doped ZnO films offer a suitable replacement for ITO in many applications such as LCD and touch screen displays.
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Polley, Todd A. "Zone model development for combustion chemical vapor deposition of zinc oxide thin films." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19565.
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Deng, Yuanyuan, and 邓远源. "Magnetic circular dichroism and Hall measurement of cobalt-doped zinc oxide thin films." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B50434494.
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The observation of ferromagnetism of (Ga,Mn)As by Ohno in 1998 has inspired great interest in diluted magnetic semiconductors (DMS). DMS’s features combining ferromagnetism and semiconducting make them of great potential for conceptual spintronic devices, which is a promising field of research for the emerging electronics. The practical application of DMS requires a Curie temperature well above room temperature and an intrinsic ferromagnetism. There are several types of DMS materials. The typical ones are transition-metal (TM) doped GaAs, GaN and ZnO. The TM-doped ZnO has drawn particular attention due to the observation of room temperature ferromagnetism in this system including cobalt-doped ZnO.But the origin of ferromagnetic TM-doped ZnO is still unknown after a decade’s theoretical and experimental effort on this material.
In this thesis, we do the magnetic circular dichroism(MCD) and Hall measurement of high quality Cobalt-doped ZnO thin films grown by molecular beam epitaxy (MBE). Room temperature ferromagnetism is observed in these samples. Combining the data from MCD and Hall measurement, we attribute the room temperature ferromagnetism in this system to the impurity band of the doped Cobalt cations.published_or_final_version
Physics
Master
Master of Philosophy
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Zou, Elva Xin. "Sol-gel processed zinc oxide for third generation photovoltaics." Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559838.
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This thesis presents an experimental study of the incorporation and optimization of sol-gel processed aluminum doped zinc oxide (AZO) thin films in solar cell devices. I first optimized the optoelectronic properties of AZO thin films by manipulating the dopant incorporation, choice of precursor chemicals and post deposition anneal treatments. Results showed that improved performance could be attributed to several factors, including improved charge carrier concentration, mobility and conductivity. AZO thin films with transmittance of over 90% and resistivity values of the order of 10-2 Ω•cm have been achieved. I also demonstrated the successful application of these AZO thin films in organic photovoltaics (OPV), to serve as an alternative to ITO electrodes. I demonstrated greater than 2-fold improvement in device efficiency through the modification of the front contact/polymer interface using zinc oxide buffer layers. This improved the charge selectivity of the electrodes and energy level alignment at the interface while reducing the recombination of separated charges and the device's series resistance. Finally, I showed that the efficiency of inverted ZnO/PbS quantum dots solar cells can be enhanced by optimizing the p-type PbS thickness, UV treating the n-type ZnO layer and exposing the devices in the dark to nitrogen. Both ZnO and AZO systems were studied, and efficiency enhancement were demonstrated for a range of Al content from 0 to O.4at.%.
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Schmidt, Matthias. "Space Charge Spectroscopy applied to Defect Studies in Ion-Implanted Zinc Oxide Thin Films." Doctoral thesis, Universitätsbibliothek Leipzig, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-84485.
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Die vorliegende Arbeit befasst sich mit der Erzeugung und Detektion von Defekten im Halbleiter Zinkoxyd (ZnO). Der Fokus liegt dabei auf der Verwendung raumladungszonenspektroskopischer Techniken zur Detektion und Charakterisierung elektronischer Defektzustände. Es werden theoretische Aspekte von Raumladungszonen an Halbleitergrenzflächen und den darin enthaltenen elektronischen Defektzuständen behandelt. Das elektrische Potential in der Raumladungszone genügt einer nichtlinearen, eindimensionalen Poissongleichung, für die bekannte, näherungsweise Lösungen vorgestellt werden. Für eine homogen dotierte Raumladungszone gelang es, die exakte Lösung des Potentialverlaufs
als Integral anzugeben und einen analytischen Ausdruck für die Kapazität
der Raumladungszone zu berechnen. Desweiteren werden transiente und oszillatorische Lösungen der Differentialgleichung zur Beschreibung der Zeitentwicklung der Besetzungswahrscheinlichkeit von Defektzuständen für verschiedene experimentelle Bedingungen betrachtet. Sämtliche raumladungszonenspektroskopischen Experimente können durch geeignete Lösungen dieser beiden Differentialgleichungen beschrieben werden. Für die Fälle, für die keine analytischen Lösungen bekannt sind, wurde ein numerisches Modell entwickelt. Die Experimente wurden an ZnO Dünnfilmproben durchgeführt, welche mittels gepulster Laserablation auf Korundsubstraten abgeschieden wurden. Zur Erzeugung von Defekten wurden entweder Ionen in die Proben implantiert, die Proben mit hochenergetischen Elektronen bzw. Protonen bestrahlt oder einer thermischen Behandlung unterzogen. Die Raumladungszonen wurden durch Schottkykontakte realisiert. Durch die raumladungszonenspektroskopischen Verfahren, Kapazitäts-Spannungs Messungen, Admittanzspektroskopie, Deep-Level Transient Spectroscopy (DLTS), Minority Carrier Transient Spectroscopy, optische DLTS, Photokapazitäts- und Photostrommessungen, sowie der optischen Kapazitäts-Spannungs Messung konnten Defektzustände in der gesamten ZnO Bandlücke nachgewiesen werden. Durch Vergleiche der gemessenen Defektkonzentrationen in einer unbehandelten Referenzprobe mit denen in behandelten Proben konnten Aussagen über die experimentellen Bedingungen, unter denen intrinsische Defekte entstehen bzw. ausheilen, gewonnen und mit Stickstoff- bzw. Nickel- in Zusammenhang stehende Defekte identifiziert werden. Für eine Vielzahl untersuchter Defektzustände konnten die thermische Aktivierungsenergie der Ladungsträgeremission, Querschnitte für den Einfang freier Ladungsträger sowie die spektralen Photoionisationsquerschnitte bestimmt werden. Aus diesen Eigenschaften sowie den experimentellen Bedingungen unter denen der Defekt bevorzugt gebildet wird, wurden Rückschlüsse auf die mikroskopische Struktur einiger Defekte gezogen.
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Song, Dengyuan Centre for Photovoltaic Engineering UNSW. "Zinc oxide TCOs (Transparent Conductive Oxides) and polycrystalline silicon thin-films for photovoltaic applications." Awarded by:University of New South Wales. Centre for Photovoltaic Engineering, 2005. http://handle.unsw.edu.au/1959.4/29371.
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Transparent conductive oxides (TCOs) and polycrystalline silicon (poly-Si) thin-films are very promising for application in photovoltaics. It is extremely challenging to develop cheap TCOs and poly-Si films to make photovoltaic devices. The aim of this thesis is to study sputtered aluminum-doped ZnO TCO and poly-Si films by solid-phase crystallization (SPC) for application in low-cost photovoltaics. The investigated aspects have been (i) to develop and characterize sputtered aluminum-doped ZnO (ZnO:Al) films that can be used as a TCO material on crystalline silicon solar cells, (ii) to explore the potential of the developed ZnO:Al films for application in ZnO:Al/c-Si heterojunction solar cells, (iii) to make and characterize poly-Si thin-films on different kinds of glass substrates by SPC using electron-beam evaporated amorphous silicon (a-Si) [referred to as EVA poly-Si material (SPC of evaporated a-Si)], and (iv) to fabricate EVA poly-Si thin-film solar cells on glass and improve the energy conversion efficiency of these cells by post-crystallization treatments. The ZnO:Al work in this thesis is focused on the correlation between film characteristics and deposition parameters, such as rf sputter power (Prf), working gas pressure (Pw), and substrate temperature (Tsub), to get a clear picture of film properties in the optimized conditions for application in photovoltaic devices. Especially the laterally non-uniform film properties resulting from the laterally inhomogeneous erosion of the target material are investigated in detail. The influence of Prf, Pw and Tsub on the structural, electrical, optical and surface morphology properties of ZnO:Al films is discussed. It is found that the lateral variations of the parameters of ZnO:Al films prepared by rf magnetron sputtering can be reduced to acceptable levels by optimising the deposition parameters. ZnO:Al/c-Si heterojunction solar cells are fabricated and characterized to demonstrate the feasibility of the fabricated ZnO:Al films for application in heterojunction solar cells. In this application, expensive indium-tin oxide (ITO) is usually used. Under the standard AM1.5G spectrum (100 mW/cm2, 25 ??C), the best fabricated cell shows an open-circuit voltage of 411 mV, a short-circuit current density of 30.0 mA/cm2, a fill factor of 66.7 %, and a conversion efficiency of 8.2 %. This is believed to be the highest stable efficiency ever reported for this type of cell. By means of dark forward current density-voltage-temperature (J-V-T) measurements, it is shown that the dominant current transport mechanism in the ZnO:Al/c-Si solar cells, in the intermediate forward bias voltage region, is trap-assisted multistep tunneling. EVA poly-Si thin-films are prepared on four types of glass substrates (planar and textured glass, both either bare or SiN-coated) based on evaporated Si, which is a cheaper Si deposition method than the existing technologies. The textured glass is realized by the UNSW-developed AIT process (AIT = aluminium-induced texture). The investigation is concentrated on finding optimized process parameters and evaluating film crystallization quality. It is found that EVA poly-Si films have a grain size in the range 0.8-1.5 ??m, and a preferential (111) orientation. UV reflectance and Raman spectroscopy measurements reveal a high crystalline material quality, both at the air-side surface and in the bulk. EVA cells are fabricated in both substrate and superstrate configuration. Special attention is paid to improving the Voc of the solar cells. For this purpose, after the SPC process, the samples receive the two post-crystallization treatments: (i) a rapid thermal anneal (RTA), and (ii) a plasma hydrogenation. It is found that two post-crystallization treatments more than double the 1-Sun Voc of the substrate-type cells. It is demonstrated that RTA improves the structural material quality of the cells. Furthermore, a hydrogenation step is shown to significantly improve the electronic material quality of the cells. Based on the RTA???d and hydrogenated EVA poly-Si material, the first mesa-type EVA cells are fabricated in substrate configuration, by using sputtered Al-doped ZnO as the transparent front contact. The investigation is focused on addressing the correlation between the type of the substrate and cell performance. Optical, electrical and photovoltaic properties of the devices are characterized. It is found that the performance of EVA cells depends on the glass substrate topography. For cells on textured glass, the AIT texture is shown to have a beneficial effect on the optical absorption of EVA films. It is demonstrated that a SiN barrier layer on the AIT-textured glass improves significantly both the crystalline quality of the poly-Si films and the energy conversion efficiency of the resulting solar cells. For cells on planar glass, a SiN film between the planar glass and the poly-Si film has no obvious effect on the cell properties. The investigations in this thesis clearly show that EVA poly-Si films are very promising for poly-Si thin-film solar cells on glass.
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Figgures, Christopher Colin. "The sputtering of zinc oxide thin films for spectrally selective solar energy material applications." Thesis, Oxford Brookes University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329488.
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Бересток, Таїсія Олександрівна, Таисия Александровна Бересток, Taisiia Oleksandrivna Berestok, Денис Ігорович Курбатов, Денис Игоревич Курбатов, Denys Ihorovych Kurbatov, Надія Миколаївна Опанасюк, et al. "Structural Properties of ZnO Thin Films Obtained by Chemical Bath Deposition Technique." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35076.
Full textAbstract:
Zinc oxide thin films have been deposited onto glass substrate from zinc sulfate, ammonia and thiourea
aqueous solution by chemical bath deposition. In the work this were specified solution preparation procedure
and optimized the composition of the solution and content of component in it. X-ray difraction and
high-resolution scanning electron microscopy were used to characterize structure formation of obtaining
ZnO films. As a result of investigation was determined the effect of time deposition on the structural and
substructural properties such as lattice parameters, texture quality, coherent scattering domain size.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35076
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Matsumura, Masashi. "Synthesis, electrical properties, and optical characterization of hybrid zinc oxide/polymer thin films and nanostructures." Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2009r/matsumura.pdf.
Full textAbstract:
Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.Title from PDF t.p. (viewed Feb. 3, 2010). Additional advisors: Derrick R. Dean, Sergey B. Mirov, Sergey Vyazovkin, Mary Ellen Zvanut. Includes bibliographical references (p. 122-145).
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Gokhale, Nikhil Suresh. "Studies On The Development Of Piezoelectric Thin Flm Based Impact Sensor." Thesis, 2008. http://hdl.handle.net/2005/770.
Full textAbstract:
Sensors is one of the major areas of current research. Thin film micro/nano sensors are gaining attention worldwide, as there is necessity of miniaturization. There are varieties of sensors available by utilizing different materials in bulk and thin film form for measuring parameters like temperature, pressure, flow, humidity etc. Apart from these, there are various sensors available to measure impact force.
Impact sensor offers potential application possibilities in robotics, aerospace, structural & mechanical engineering and related areas. Many physical principles have been explored for the realization of impact sensor. The present thesis reports the efforts made in developing impact sensor using piezoelectric thin film. The necessary brief background information on impact sensors is presented in Chapter 1. This includes the description of available literature on impact sensors and their probable applications. In Chapter 2, a review of the various techniques such as thin film deposition techniques, film thickness measurement techniques, thin film characterization techniques, used in our work are explained in detail. Chapter 3 explains the direct and indirect methods of characterization used for confirming the piezoelectric property of zinc oxide thin films. The detailed experimental work carried out in realizing the impact sensor using piezoelectric thin films is presented in chapter 4. This includes design of the sensor, calibration setup used & the procedure followed and results obtained.
Finally, we present the summary of the work carried out in the thesis, conclusions arrived at and the scope for carrying out further work in the direction of making the sensor more efficient.
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Joshi, Sudeep. "Towards Flexible Sensors and Actuators : Application Aspect of Piezoelectronic Thin Film." Thesis, 2013. http://etd.iisc.ernet.in/2005/3431.
Full textAbstract:
Man’s desire to replicate/mimic the nature’s creation provided an impetus and inspiration to the rapid advancements and progress made in the sensors and actuators technology. A normal human being has five basic sensory organs, which helps and guides him in performing the routine tasks. This underlines the importance of basic sensory organs in a human life. In a similar fashion, sensors and actuators are of paramount importance for most of the science and engineering applications.
The aim of the present thesis work is to explore the application of piezoelectric ZnO thin films deposited on a flexible substrate for the development of sensors and actuators. Detailed study was performed on the suitability of three different flexible substrates namely Phynox, Kapton and Mylar. However, Phynox alloy substrate was found to be a suitable substrate material for the above mentioned applications. Sputtering technique was chosen for the deposition of ZnO thin films on to Phynox substrate. The necessary process parameters were optimized to achieve good quality piezoelectric thin films.
In the present work, sensors have been developed by utilizing the direct piezoelectric effect of ZnO thin films deposited on Phynox alloy substrate. These includes a flow sensor for gas flow rate measurement, impact sensor for non-destructive material discrimination study and a Thin Film Sensor Array (TFSA) for monitoring the impact events. On the other hand, using the converse piezoelectric effect of ZnO thin films, actuators have also been developed. These include a thin film micro actuator and a Thin Film Micro Vibrator (TFMV) for vibration testing of micro devices. The thesis is divided into following seven chapters.
Chapter 1:
This chapter gives a general introduction about sensors and actuators, piezoelectric thin films, flexible substrates, thin film deposition processes and characterization techniques. A brief literature survey of different applications of piezoelectric thin films deposited on various flexible substrates in device development is presented.
Chapter 2:
A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. ZnO thin films were deposited on Phynox substrate by Rf reactive magnetron sputtering technique. The sputtering process parameters such as: Ar:O2 gas ratio, substrate temperature and RF power were optimized for the deposition of good quality piezoelectric ZnO thin films. The deposited ZnO thin films were characterized using XRD, SEM, AFM and d31 coefficient measurement techniques.
Chapter 3:
It reports on the comparative study of properties of piezoelectric ZnO thin films deposited on three different types of flexible substrates. The substrate materials employed were a metal alloy (Phynox), polyimide (Kapton), and polyester (Mylar). Piezoelectric ZnO thin films deposited on these flexible substrates were characterized by XRD, SEM, AFM and d31 coefficient measurement techniques. A vibration sensing test was also performed for the confirmation of good piezoelectric property. Compared to the polymer flexible substrates, the metal alloy flexible substrate (Phynox) was found to be more suitable for integrating ZnO thin film for sensing applications.
Chapter 4:
The development of a novel gas flow sensor for the flow rate measurement in the range of L min-1 is presented in this chapter. The sensing element is a Phynox alloy cantilever integrated with piezoelectric ZnO thin film. A detailed theoretical analysis of the experimental set–up showing the relationship between output voltage generated and force at a particular flow rate has been discussed. The flow sensor is calibrated using an in-house developed testing set-up.
Chapter 5:
This chapter is divided into two sections. Section 5.1 reports on the development of a novel packaged piezoelectric thin film impact sensor and its application in non-destructive material discrimination studies. Different materials (Iron, Glass, Wood and Plastic) were successfully discriminated by using the developed impact sensor. The output response of impact sensor showed good linearity and repeatability. The impact sensor is sensitive, reliable and cost-effective. Section 5.2 reports on the development of a Thin Film Senor Array (TFSA) for monitoring the location and magnitude of the impact force. The fabricated TFSA consists of evenly distributed ZnO thin film sensor array.
Chapter 6:
It consists of two sections. Section 6.1 reports on the fabrication of micro actuator using piezoelectric ZnO thin film integrated with flexible Phynox substrate. A suitable concave Perspex mounting was designed for the actuator element. The actuator element was excited at different frequencies for the supply voltages of 2V, 5V and 8V. The developed micro actuator has the potential to be used as a micro pump for pumping nano liters to micro liters of fluids. Section 6.2 reports the design and development of a portable ready to use Thin Film Micro Vibrator (TFMV). The TFMV is capable of providing the vibration amplitude in the range of nanometer to micrometer. A thin silicon diaphragm was used as a test specimen for its vibration testing studies using the developed TFMV. The TFMV is light-weight and have internal battery, hence no external power supply is required for its functioning.
Chapter 7:
The first section summarizes the salient features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.
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"Zinc Oxide Transparent Thin Films For Optoelectronics." Doctoral diss., 2010. http://hdl.handle.net/2286/R.I.8636.
Full textAbstract:
abstract: The object of this body of work is to study the properties and suitability of zinc oxide thin films with a view to engineering them for optoelectronics applications, making them a cheap and effective alternative to indium tin oxide (ITO), the most used transparent conducting oxides in the industry. Initially, a study was undertaken to examine the behavior of silver contacts to ZnO and ITO during thermal processing, a step frequently used in materials processing in optoelectronics. The second study involved an attempt to improve the conductivity of ZnO films by inserting a thin copper layer between two ZnO layers. The Hall resistivity of the films was as low as 6.9×10-5 -cm with a carrier concentration of 1.2×1022 cm-3 at the optimum copper layer thickness. The physics of conduction in the films has been examined. In order to improve the average visible transmittance, we replaced the copper layer with gold. The films were then found to undergo a seven orders of magnitude drop in effective resistivity from 200 -cm to 5.2×10-5 -cm The films have an average transmittance between 75% and 85% depending upon the gold thickness, and a peak transmittance of up to 93%. The best Haacke figure of merit was 15.1×10-3 . Finally, to test the multilayer transparent electrodes on a device, ZnO/Au/ZnO (ZAZ) electrodes were evaluated as transparent electrodes for organic light-emitting devices (OLEDs). The electrodes exhibited substantially enhanced conductivity (about 8×10-5 -cm) over conventional indium tin oxide (ITO) electrodes (about 3.2×10-5 -cm). OLEDs fabricated with the ZAZ electrodes showed reduced leakage compared to control OLEDs on ITO and reduced ohmic losses at high current densities. At a luminance of 25000 cd/m2, the lum/W efficiency of the ZAZ electrode based device improved by 5% compared to the device on ITO. A normalized intensity graph of the colour output from the green OLEDs shows that ZAZ electrodes allow for a broader spectral output in the green wavelength region of peak photopic sensitivity compared to ITO. The results have implications for electrode choice in display technology.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2010
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Kekuda, Dhananjaya. "Property Modulation Of Zinc Oxide Through Doping." Thesis, 2007. http://hdl.handle.net/2005/465.
Full textAbstract:
Semi conductors are of technological importance and attracted many of the re-searchers. ZnO belongs to the family of II-VI semiconductors and has material properties well suitable to UV light emitters, varistors, Schottky diodes, gas sensors, spintronics, ferroelectric devices and thin film transistors. It has been considered as a competitor to GaN, which belongs to the family of III-V semiconductors. This is due to the fact that ZnO of high quality can be deposited at lower growth temperatures than GaN, leading to the possibility of transparent junctions on less expensive substrates such as glass. This will lead to low-cost UV lasers with important applications in high-density data storage systems etc. One of the most popular growth techniques of ZnO is physical sputtering. As compared to sol-gel and chemical-vapor deposition, the magnetron sputtering is a preferred method because of its simplicity and low operating temperatures. Hence, detailed investigations were carried out on undoped and doped ZnO thin films primarily deposited by magnetron sputtering. The obtained results in the present work are presented in the form of a thesis.
Chapter 1: A brief discussion on the crystal structure of ZnO material and its possible applications in the different areas such as Schottky diodes, spintronics, ferroelectric devices and thin film transistors are presented.
Chapter 2: This chapter deals with various deposition techniques used in the present study. It includes the magnetron sputtering, thermal oxidation, pulsed-laser ablation and sol-gel technique. The experimental set up details and the deposition procedures are described in detail i.e., the deposition principle and the parameters that will affect the film properties. A brief note on the structural characterization equipments namely, X-ray diffraction, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and the optical characterization equipments namely, transmission spectroscopy is presented. The transport properties of the films were studied which include Dielectric studies, impedance studies, device characterization and are discussed.
Chapter 3: The optimization of ZnO thin films for Schottky diode formation and
The characterization of various Schottky diodes is presented in this chapter. P-type conductivity in ZnO was implemented by the variation of partial pressure of oxygen during the sputtering and are discussed. A method to achieve low series resistance hetero-junction was achieved using thermal oxidation method and the detailed transport properties were studied. The optical investigation carried out on the ZnO thin films under various growth conditions are also presented.
Chapter 4: This chapter deals with the processing, structural, electrical, optical and magnetic properties of Mn doped ZnO thin films grown by pulsed laser ablation. Structural investigations have shown that the Mn incorporation increases the c-axis length due to the relatively larger ionic size of the Mn ions. Studies conducted both at low and high concentration region of Zn1¡xMnxO thin films showed that the films are anti-ferromagnetic in nature. The transport measurements revealed that the electrical conductivity is dominated by the presence of shallow traps. Optical investigations suggested the absence of midgap absorption and confirm the uniform distribution of Mn in wurtzite structure.
Chapter 5: Carrier induced ferromagnetism in Co doped ZnO thin films were studied and the results are presented in this chapter. High density targets were prepared by solid state reaction process and the thin films were deposited by pulsed laser ablation technique. Two compositions were studied and it was found that with increase in substrate temperature, c-axis length decreases. Optical studies suggested a strong mid gap absorption around 2eV and could be attributed to the d-d transitions of tetrahedral coordinated Co2+. The presence of ferromagnetism in these films makes them potential candidates for spintronics applications.
Chapter 6: It has been reported in literature that o®-centered polarization will drive ferroelectric phase transition. Motivated by such results, substitution of Lithium in ZnO was studied in detail. The structural and electrical properties were investigated over a wide range of composition (0-25%). The ferroelectric studies were carried out both in metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) configuration and are presented in this chapter. The appearance of Ferro electricity in these films makes them potential candidates for ferroelectric memory devices.
Chapter 7: This chapter describes the studies conducted on Mg doped ZnO
Thin films grown by multi-magnetron sputtering. The hexagonal phases of the films were evaluated. All the films exhibited c-axis preferred orientation towards (002) orientation. Micro structural evolutions of the films were carried out through scanning electron microscopy and atomic force microscopy. Ferroelectric properties were investigated in both metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) configurations. It was observed that the Mg concentration increases the band gap and the details on optical investigations are also presented in this chapter.
Chapter 8: ZnO based thin film transistors have been fabricated and characterized using ZnO as active channel layer and Mg doped ZnO as dielectric layer. Excellent leakage properties of the gate dielectric were studied and presented in this chapter. These studies demonstrated that Mg doped ZnO thin films are suitable candidates for gate dielectric applications.
Conclusions: This section presents the conclusions derived out of the present work. It also includes a few suggestions on future work on this material.
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CHAN, CHANG-EN, and 詹長恩. "Fabrication of Zinc Oxide Thin Films by MOCVD." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/78644047771879366742.
Full textAbstract:
碩士中原大學
電子工程研究所
96
Zinc oxide ( ZnO ), one of II-VI compound semiconductors can be used to fabricate ultraviolet light emitting diodes ( UV-LEDs ), window layers for solar cells and front electrodes for liquid crystal display ( LCD ). ZnO films were grown successfully on Si substrates with a low-temperature grown ZnO nucleation layers by metal organic chemical vapor deposition ( MOCVD ). The structure and surface morphology were characterized by X-ray diffraction ( XRD ), field emission scanning electron microscopy ( FE-SEM ) and atomic force microscopy ( AFM ). Optical and electrical properties were examined by photoluminescence ( PL ), and Hall effect measurements, respectively. Impurity distribution in the film was investigated by secondary ion mass spectrometry ( SIMS ). The Si substrate of ( 111 ) orientation and the growth temperature of 400℃ could be used to obtain the ZnO films with the optimal crystalline, optical and electrical properties. N-type ZnO films were fabricated with the doping of gallium ( Ga ), aluminum ( Al ) and indium ( In ). The Al-doped films showed the most stable electrical properties compared with other n-type doped films. A sheet resistivity of 426.7 /sq and an electron carrier concentration of 5.27×1019cm-3 were achieved for these Al-doped films. On the other hand, p-type ZnO was fabricated by doping the films with arsenic ( As ). Low temperature PL measurements recognized the donor-acceptor pair (DAP) emission characteristics of our As-doped ZnO films, which presents a proof for the successful formation of p-type ZnO. Based on this result, the fabrication of ZnO homojunction has been completed.
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Tsai, Chung-Yun, and 蔡忠育. "Fabrication and Characterization of Zinc Oxide Thin Films." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/4938y9.
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碩士國立臺北科技大學
製造科技研究所
97
The contents of this study were roughly divided into two stages. In the first stage, ZnO nanoparticles were prepared by the sol-gel method. After prepared, oxide powders, which were examined by XRD and SAED analyses, were proved to possess a hexagonal wurtzite ZnO structure. In addition, when ZnO nanoparticles were sintered at different temperature on a silicon wafer by spin coating, ZnO nanoparticles could achieve sintered densification at about 900 ℃. The prepared Zinc oxide nanoparticles required the minimum activation energy when added 4ml NaOH. And the activation energy of grain of ZnO powders was 113.66 KJ/mol. The crystal quality of powders was improved by annealing. In this paper, the peak of ZnO nanoparticles was single. However, the peak of micro zno powders was double due to their surface shapes. UV / VIS spectroscopy could confirm that the increased amount of NaOH would influence the UV absorption band. Moreover, with the increase of NaOH, the wavelength of ZnO nanoparticles UV absorption band would move to the long wavelength. The result indirectly confirmed that three types of powders were different due to the sizes of particles. The second stage was about preparaed zinc oxide thin films, discussing the influence of annealing temperature on them. By XRD and Raman spectroscopy analyses, the crystal quality of films was found to be improved because of annealing, but their tensile stresses rose with the increases of annealing temperature due to the oxygen vacancy, which was confirmed by the Raman spectroscopyhas. As Oxygen vacancies would affect the electrical properties, the resistivity decreases with the increases of annealing temperature. When ZnO thin films were irradiated by UV light, with the increase of exposure time, the zno contact angle turned from hydrophobic to hydrophilic interaction. In addition, the contact angle and UV / VIS absorption spectra of the intensity showed that the effects of spin-coating zinc oxide on ITO glass on UV light were more significant. Therefore, the UV light for the result of the zinc oxide thin film capacitors and ultra-violet absorption spectrum was inferred to be a positive relationship.
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簡志峰. "Growth of Zinc Oxide and Zinc Gadolinium Oxide Thin Films by Pulsed Laser Deposition." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/71336766014846956733.
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lo, Chih-neng, and 羅智能. "Fabrication and Characterization of Electrochemical Deposition Zinc Oxide and Indium Doped Zinc Oxide Thin Films." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/68323977972125371801.
Full textAbstract:
碩士逢甲大學
資訊電機工程碩士在職專班
99
In this thesis, the zinc oxide (ZnO) thin films was fabricated form zinc films deposited on ITO/glass substrates by electrodeposition technique. The zinc thin film is electrodepositioned by using an aqueous solution of 0.1 M Zn(NO3)2 and 0.1 M H3BO3 with a pH value approximately 4.1. The ZnO thin films were annealed in air for the temperatures form 300 to 500 ℃.The effect of annealing on the structure and morphology of thin film are studied. X-ray diffraction patterns showed that the annealing at 500 ℃ can convert these films to ZnO. Zinc oxide (ZnO) thin films and Indium doped Zinc Oxide (IZO) thin films were electrodeposition on ITO/glass substrates in an electrochemical cell containing an aqueous solution. The ZnO thin film is electrodepositioned by using an aqueous solution of 0.05 M Zn(NO3)2 and 0.01 M HMTA with a pH value approximately 6.4. The IZO thin film is electrodepositioned by using an aqueous solution of 0.05 M Zn(NO3)2, 1 mM to 10 mM InCl3 and 0.01 M HMTA with a pH value approximately 3.4 to 5.6. The deposition parameters include the deposition potential, deposition temperature, deposition time and different InCl3 concentrations. The crystal structures of the films were identified by X-ray diffraction utilizing Cu K?radiation. The surface morphology and composition of films were investigated by SEM micrographs and EDS analysis, respectively.
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Hsieh, Hsiu-ming, and 謝修銘. "High-Humidity Study on Aluminum Doped Zinc Oxide Thin Films." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/57792940194528423114.
Full textAbstract:
碩士國立中央大學
化學工程與材料工程研究所
98
This study focuses on the electrical and optical stability of AZO (ZnO: Al2O3= 98 wt.% : 2 wt.%) transparent conductive thin film in high humidity environment, and discusses their behavior in different annealing ambient (vacuum and oxygen). In this experiment, we use the RF-magnetron sputter system to deposit the thin films on the quartz substrate. After deposition, there are two different annealing ambient is applied, which are vacuum and oxygen. Finally, these samples were put in a high humidity environmental test system. Using Hall Measurement and 4-points probe stage to measure the change of the electrical properties, the UV/VIS Spectrophotometer used to monitor the transmittance. From the X-ray Photoelectron Spectroscopy result, we can observe the change of the binding energy or chemical state in AZO thin films about each element, like zinc and oxygen. According to AZO films annealed in different atmospheres (vacuum, oxygen), the trends of resistivity change show big differences among them. There are two effects (annealing ambient and surface adsorption of water molecules) causing an oxygen concentration gradient along the film thickness. When the oxygen vacancy is the dominate mechanism of the carrier formation, the moisture will cause a serious decay of electrical property due to the annihilation of free carriers. From the second part of results, the Cr-coated AZO structure can exhibit a great electrical property and stability. It shows a 90 % transmittance in visible region. It might be a suitable candidate to replace ITO in the application of those products used in harsh environmental conditions.
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Chang, Yu-Shan, and 張玉珊. "Preparation and Characterization of Electrodeposition for Zinc Oxide Thin Films." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/57585766644818827126.
Full textAbstract:
碩士國立高雄海洋科技大學
微電子工程研究所
100
In this study, the ZnO thin film is grown onto an ITO glass substrate by electrodeposition and is analyzed by XRD, SEM and PL. The electrodepositon device is carried out in two electrodes systems where the ITO glass is used as the working electrode with an electrolyte containing Zn(NO3)2 aqueous solution. After deposition, the thin film is annealed for 1 hour at 250, 300, 350 and 400 °C, respectively. The electrodeposition has many advantages, such as low cost, simple processing and low temperature prerequisites. The study discovered that when the concentration increases (0.005M~0.1M), the reactants' concentration before heating increases disproportionately and changes their structure types. During the experiment, the deposition current affected the density of the structure. (002) preferential orientation and polycrystalline wurtzite structure is observed in XRD pattern of zinc oxide by plating deposition. From the results of the PL sepctroscopy, it can be seen that through applying the appropriate temperature and treatment process, the UV's and green light's ratio of intensity increased by nearly 30 times the original value and showed reduction of the level of defects. Size increases with annealing temperature proportionally. However, due to the high temperature, the bonds grow weaker resulting in the attenuation of the UV's intensity. Therefore, changing the electroplating parameters and appropriate heat treatment temperature, really can prepare nano-zinc oxide structure.
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Sheu, Cheng-Wei, and 徐政維. "Study of metal electrode contacts to Zinc Oxide thin films." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/9qnww4.
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碩士國立虎尾科技大學
光電與材料科技研究所
96
To accomplish high-performance ZnO-based optoelectronic devices, the formation of high quality metal electrode contacts is essential. A superior rectifying junction with metals and low-resistance ohmic contacts onto the ZnO surface was the best mechanism that promoted their use in diode, UV detector, gas sensor, piezoelectric transducer, and optical applications . There were many reports addressing the mechanisms for the difficulties in the formation of ZnO-based Schottky diodes, including surface morphology, environment activity and subsurface defects . A variety of ZnO surface treatment methods, such as chemical preparation with acid, plasma or irradiation treatments, and surface passivation via a chemical solution were demonstrated to removal the interfacial states of the metal Schottky contact to ZnO. To date, magnetron sputtering is a commonly used system for deposition crystalline ZnO films in application on the optoelectronic devices. However, there were very limited reports on Schottky contacts of ZnO, especially for that of sputtered-ZnO thin films. In this study, the 2 μm-thick undoped-ZnO film was deposited onto silicon substrate using rf magnetron sputtering system and then annealed at 700oC for 30 min under oxygen ambient to achieve a superior c-axis orientation with oxygen-terminated crystalline structure. The films were undoped but show n-type conduction (~ 3.83 ? 1011 cm-3). Ni/Au and Al were respectively, employed to form Schottky and ohmic contact on the ZnO-based structures. These contact metals patterned directly by lift-off of evaporated films onto the ZnO film was denoted as the conventional Schottky diode (sample A), whereas that of the Schottky contact surface processed with an additive oxygen plasma treatment at 270 W for 10 min prior to metal deposition was classified as sample B. In addition to the conventional Schottky diode structure, another set of multilayer Schottky diode structure (sample C) with a homogeneity ITO-ZnO cosputtered layer (~ 250 nm) deposited onto the undoped-ZnO film also prepared to improve the ohmic contact performance. The ITO-ZnO cosputtered film at an atomic ratio of 90% [Zn / (Zn + In) at.%] was annealed at 300oC for 30 min under oxygen ambient and possessed an electron carrier concentration of 7.01 ? 1018 cm-3 . Detail structures of the conventional and multilayer Schottky diodes structures are illustrated in Fig. Carrier concentration and hall mobility of the deposited films were measured by the van der Pauw method. The crystalline structures and surface morphologies were examined by XRD and AFM measurements. Current-voltage properties of these Schottky diode structures were characterized using semiconductor parameter analyzer (HP4156C). A comparison for the I-V characteristic of Ni/Au Schottky contacts to the undoped-ZnO surface with and without oxygen plasma process is shown. Both the reverse and forward currents of the conventional Schottky diode were markedly reduced after processing with an additive oxygen plasma treatment. In addition, the ratios of the forward to leakage current measured at -2 and 2 V were also increased from 4.78 (sample A) to 14.25 (sample B), indicating a better rectifying behavior. The convention Schottky diode had a high ideality factor (n) of 2.47, meaning that the existence of multiple current pathways other than thermionic emission. In contrast, the ideality factor and barrier height (ΦB) were evaluated to be 1.92 and 0.82 eV, respectively. The reduction in the ideality factor as well as the increase in the barrier height performances was consisted with the report that addressed to be the donor-like defect passivation of the oxygen radical in the plasma diffused into the host lattice in the ZnO films surface . Although the rectifying behavior had been significant improved through the oxygen plasma treatment on the Schottky contact surface, the forward current was too small due to the poor ohmic contact behavior. The specific contact resistance was greatly decreased to 1.44 ? 10-3 ? cm2 with a homogeneity ITO-ZnO cosputtered film deposited onto the undoped-ZnO film. Elimination of surface carbon- and hydrogen-related contaminations as well as the compensation of the oxygen-related vacancies reduced not only the defect-assisted tunneling of electron but also the net carrier concentration at the Ni/ZnO surface leading to the better Schottky diodes performance.
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Huang, Chung-Chieh, and 黃崇傑. "Fabrication and characterization ofIndium-Zinc oxide thin films by sputtering." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/uah3kf.
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碩士國立虎尾科技大學
光電與材料科技研究所
95
Abstract TCO (transparent conductive oxide) is widely used in the optoelectronics, such as solar cells, flat panel display (FPD), and touch panel due to their high visible light transmission and great electrical conductivity. The main purpose of TCO is usually employed as the transparent electrode. These kinds of materials include indium tin oxides (ITO), indium zinc oxides (IZO), and etc. Currently, ITO is the material which is widely used in the industry. However, IZO thin films have great potentials to replace ITO thin films due to it can be deposited at lower temperature while maintaining high visible light transmittance and high electrical conductivity. This low temperature processing capability allows IZO thin films to be applied in many fields, especially the flexible substrate. The experiment result shows that the IZO thin film which was deposited at room temperature with DC power 100 W has the superior property. The film shows the low resistivity of 6E-4 Ω-cm, and high transmission of 90 %. Using the low temperature sputtering process, IZO thin film will be employed for the PLED electrode and deposited on flexible substrate.
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Chirakkara, Saraswathi. "Tuning Zinc Oxide Layers Towards White Light Emission." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2324.
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White light emitting diodes (LED) have drawn increasing attention due to their low energy consumption, high efficiency and potential to become primary lighting source by replacing conventional light sources. White light emission is usually generated either by coating yellow phosphor on a blue-LED or blending red, green and blue phosphor in an appropriate ratio. Maintaining appropriate proportions of individual components in the blend is difficult and the major demerit of such system is the overall self-absorption, which changes the solution concentration. This results in uncontrolled changes in the whiteness of the emitted light. Zinc Oxide (ZnO), a wide bandgap semiconductor with a large exciton binding energy at room temperature has been recognized as a promising material for ultraviolet LEDs and laser diodes. Tuning of structural, optical and electrical properties of ZnO thin films by different dopants (Lithium, Indium and Gallium) is dealt in this thesis. The achievement of white light emission from a semiconducting material without using phosphors offers an inexpensive fabrication technology, good luminescence, low turn-on voltage and high efficiency.
The present work is organized chapter wise, which has 8 chapters including the summary and future work.
Chapter 1: Gives a brief discussion on the overview of ZnO as an optoelectronic material, crystal structure of semiconductor ZnO, the effect of doping, optical properties and its possible applications in optoelectronic devices.
Chapter 2: Deals with various deposition techniques used in the present study, includes pulsed laser deposition and thermal evaporation. The experimental set up details and the deposition procedures are described in detail. A brief note on the structural characterization equipments, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and the optical characterization techniques namely Raman spectroscopy, transmission spectroscopy and photoluminescence (PL) spectroscopy is presented. The electrical properties of the films were studied by current- voltage, capacitance - voltage and Hall Effect measurements and the experimental details are discussed.
Chapter 3: High quality ZnO/Si heterojunctions fabricated by growing ZnO thin films on p-type Si (100) substrate by pulsed laser deposition without using buffer layers are discussed in this chapter. The crystallinity of the heterojunction was analyzed by high resolution X-ray diffraction and atomic force microscopy. The optical quality of the film was analyzed by room temperature (RT) photoluminescence measurements. The high intense band to band emission confirmed the high quality of the ZnO thin films on Si. The electrical properties of the junction were studied by temperature dependent resistivity, current- voltage measurements and RT capacitance-voltage (C-V) analysis. ZnO thin film showed the lowest resistivity of 6.4x10-3 Ω.cm, mobility of 7 cm2/V.sec and charge carrier concentration of 1.58x1019cm-3 at RT. The charge carrier concentration and the barrier height (BH) were calculated to be 9.7x1019cm-3 and 0.6 eV respectively from the C-V plot. The BH and ideality factor, calculated by using the thermionic emission (TE) model were found to be highly temperature dependent. We observed a much lower value in Richardson constant, 5.19x10-7 A/cm2K2 than the theoretical value (32 A/cm2K2) for ZnO. This analysis revealed the existence of a Gaussian distribution (GD) with a standard deviation of σ2=0.035 V. By implementing GD to the TE, the values of BH and Richardson constant were obtained as 1.3 eV and 39.97 A/cm2K2 respectively from the modified Richardson plot. The obtained Richardson constant value is close to the theoretical value for n-ZnO. These high quality heterojunctions can be used for solar cell applications.
Chapter 4: This chapter describes the structural and optical properties of Li doped ZnO thin films and the properties of ZnO/Li doped ZnO multilayered thin film structures. Thin films of ZnO, Li doped ZnO (ZLO) and multilayer of ZnO and ZLO (ZnO/ZLO) were grown on silicon and Corning glass substrates by pulsed laser deposition technique. Single phase formation and the crystalline qualities of the films were analyzed by X-ray diffraction and Li composition in the film was investigated to be 15 Wt % by X-ray photoelectron spectroscopy. Raman spectrum reveals the hexagonal wurtzite structure of ZnO, ZLO and ZnO/ZLO multilayer, confirms the single phase formation. Films grown on Corning glass show more than 80 % transmittance in the visible region and the optical band gaps were calculated to be 3.245, 3.26 and 3.22 eV for ZnO, ZLO and ZnO/ZLO respectively. An efficient blue emission was observed in all films that were grown on silicon (100) substrate by photoluminescence (PL). PL measurements at different temperatures reveal that the PL emission intensity of ZnO/ZLO multilayer was weakly dependent on temperature as compared to the single layers of ZnO and ZLO and the wavelength of emission was independent of temperature. Our results indicate that ZnO/ZLO multilayer can be used for the fabrication of blue light emitting diodes.
Chapter 5: This chapter is divided in to two parts. The fabrication and characterization of In doped ZnO thin films grown on Corning glass substrate is discussed in the first section. Zinc Oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along the c-direction with wurtzite structure and are highly transparent with an average transmittance of more than 80 % in the visible wavelength region. The energy band gap was found to be decreasing with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to be decreasing initially with doping concentration and subsequently increasing. The XPS and Raman spectrum confirm the presence of indium in indium doped ZnO thin films. The photoluminescence spectrum showed a tunable red light emission with different In concentrations.
Undoped and In doped ZnO (IZO) thin films were grown on Pt coated silicon substrates (Pt/Si) to fabricate Pt/ZnO:Inx Schottky contacts (SC) is discussed in the second section. The SCs were investigated by conventional two probe current-voltage (I-V) measurement and by the I-V spectroscopy of conductive atomic force microscopy (C-AFM). X-ray diffraction technique was used to examine the thin film quality. Changes in various parameters like Schottky barrier height (SBH) and ideality factor (IF) as a function of temperature were presented. The estimated BH was found to be increasing and the IF was found to be decreasing with increase in temperature. The variation of SBH and IF with temperature has been explained by considering the lateral inhomogeneities in nanometer scale lengths at metal–semiconductor (MS) interface. The inhomogeneities of SBH in nanometer scale length were confirmed by C-AFM. The SBH and IF estimated from I-V spectroscopy of C-AFM showed large deviation from the conventional two probe I-V measurements. IZO thin films showed a decrease in SBH, lower turn on voltage and an enhancement in forward current with increase in In concentration.
Chapter 6: In this chapter the properties of Ga doped ZnO thin films with different Ga concentrations along with undoped ZnO as a reference is discussed. Undoped and Ga doped ZnO thin films with different Ga concentrations were grown on Corning glass substrates by PLD. The structural, optical and electrical properties of Ga doped ZnO thin films are discussed. The XRD, XPS and Raman spectrum reveal the phase formation and successful doping of Ga on ZnO. All the films show good transmittance in the visible region and the photoluminescence of Ga doped ZnO showed a stable emission in the blue- green region. The resistivity of Ga doped ZnO thin films was found to be first decreasing and then increasing with increase in Ga concentrations.
Chapter 7: The effect of co-doping to ZnO on the structural, optical and electrical properties was described in this chapter. Ga and In co-doped ZnO (GIZO) thin films together with ZnO, In doped ZnO (IZO), Ga doped ZnO (GZO), IZO/GZO multilayer for comparison, were grown on Corning glass and boron doped Si substrates by PLD. GIZO showed better structural, optical and electrical properties compared with other thin films. The Photoluminescence spectra of GIZO showed a strong white light emission and the current-voltage characteristics showed relatively lower turn on voltage and larger forward current. The CIE co-ordinates for GIZO were observed to be (0.31, 0.33) with a CCT of 6650 K, indicating a cool white light and established a possibility of white light emitting diodes.
Finally the chapter 8 presents the summary derived out of the work and a few suggestions on future work.
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Myers, Michelle Anne. "Processing and Characterization of P-Type Doped Zinc Oxide Thin Films." Thesis, 2013. http://hdl.handle.net/1969.1/149354.
Full textAbstract:
Applications of zinc oxide (ZnO) for optoelectronic devices, including light emitting diodes, semiconductor lasers, and solar cells have not yet been realized due to the lack of high-quality p-type ZnO. In the research presented herein, pulsed laser deposition is employed to grow Ag-doped ZnO thin films, which are characterized in an attempt to understand the ability of Ag to act as a p-type dopant. By correlating the effects of the substrate temperature, oxygen pressure, and laser energy on the electrical and microstructural properties of Ag-doped ZnO films grown on c-cut sapphire substrates, p-type conductivity is achieved under elevated substrate temperatures. Characteristic stacking fault features have been continuously observed by transmission electron microscopy in all of the p-type films. Photoluminescence studies on n-type and p-type Ag-doped ZnO thin films demonstrate the role of stacking faults in determining the conductivity of the films. Exciton emission attributed to basal plane stacking faults suggests that the acceptor impurities are localized nearby the stacking faults in the n-type films. The photoluminescence investigation provides a correlation between microstructural characteristics and electrical properties of Ag- doped ZnO thin films; a link that enables further understanding of the doping nature of Ag impurities in ZnO. Under optimized deposition conditions, various substrates are investigated as potential candidates for ZnO thin film growth, including r -cut sapphire, quartz, and amorphous glass. Electrical results indicated that despite narrow conditions for obtaining p-type conductivity at a given substrate temperature, flexibility in substrate choice enables improved electrical properties.
In parallel, N+-ion implantation at elevated temperatures is explored as an alternative approach to achieve p-type ZnO. The ion implantation fluence and temperature have been optimized to achieve p-type conductivity. Transmission electron microscopy reveals that characteristic stacking fault features are present throughout the p-type films, however in n-type N-doped films high-density defect clusters are observed. These results suggest that the temperature under which ion implantation is performed plays a critical role in determining the amount of dynamic defect re- combination that can take place, as well as defect cluster formation processes. Ion implantation at elevated temperatures is shown to be an effective method to introduce increased concentrations of p-type N dopants while reducing the amount of stable post-implantation disorder.
Finally, the fabrication and properties of p-type Ag-doped ZnO/n-type ZnO and p-type N-doped ZnO/n-type ZnO thin film junctions were reported. For the N-doped sample, a rectifying behavior was observed in the I-V curve, consistent with N-doped ZnO being p-type and forming a p-n junction. The turn-on voltage of the device was ∼2.3 V under forward bias. The Ag-doped samples did not result in rectifying behavior as a result of conversion of the p-type layer to n-type behavior under the n- type layer deposition conditions. The systematic studies in this dissertation provide possible routes to grow p-type Ag-doped ZnO films and in-situ thermal activation of N-implanted dopant ions, to overcome the growth temperature limits, and to push one step closer to the future integration of ZnO-based devices.