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1
Chen, Thomas D. (Thomas Duhwa). "Electrically active defects in zinc oxide." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10997.
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Adhikari, Naresh. "Defects and Optoelectronic properties of Zinc oxide." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1562770832047501.
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3
Jokela, Slade Joseph. "Stability and structure of hydrogen defects in zinc oxide." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/s_jokela_122106.pdf.
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Thapa, Sunil. "Defects and Ferromagnetism in Transition Metal Doped Zinc Oxide." Bowling Green State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1467319340.
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Wang, Zilan, and 王子蘭. "Defect emission of ZnO and its related origins." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/211111.
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Zinc oxide (ZnO) is a promising material for ultra-violet optoelectronics applications due to its direct band gap and large exciton binding energy. Defect in semiconductor plays an important role in determining the optical and electrical properties. It is thus crucial to understand the defects‟ performance for realizing the device fabrication. Green luminescence (GL) having the peak at 2.4-2.5 eV is a defect related emission band commonly found in the luminescence spectra of many of the ZnO materials.
Despite of the effort devoted for several decades, its origin and emission mechanism remain controversial. In this thesis, the origin of the GL emitted from the ZnO films grown by pulsed laser deposition (PLD) is studied using a comprehensive spectroscopic approach, including the Hall effect measurement, photoluminescence (PL), Raman spectroscopy, positron annihilation spectroscopy (PAS), and secondary ion mass spectroscopy (SIMS).
ZnO thin films are grown by PLD method with the growth parameters (namely the substrate temperature and oxygen pressure during the growth) systemically varied. Annealing studies in argon atmosphere reveal the correlation between the free electron concentration and the hydrogen concentration in the samples. Two oxygen deficient defect related Raman modes are also identified and they anneal out after annealing at high temperature.
We have investigated the introduction the GL systematically grown by different growth parameters, undergone different post-growth annealing treatment, and different methods of growth. Two kinds of GL’s are identified. The first kind of GLs has peak at 2.47 eV without the fine structure, and the other has the peak at 2.45 eV having the fine structure of separation of 0.07 eV. The GL with the fine structure is originated from the surficial region of the ZnO film.
The GL without the fine structure is introduced after the annealing 900℃ irrespective of the initial growth conditions. PAS results show a strong correlation between the thermal introductions of a kind of Zn-vacancy and the GL without the fine structure. Moreover, a donor-acceptor-pair (DAP) emission is induced in the low temperature PL spectrum after the same annealing temperature of 900℃. The GL and the DAP emissions are thus associated with the involvement of the VZn. Furthermore by comparing the photon energies of the GL and DAP with the previous first principle calculated results, the GL is ascribed to the conduction band to the (-/2-) acceptor level of VZn, and the DAP involves the (0/-) acceptor level of VZn The presence of the conduction band to the (0/-) level transition is compatible with the results of the photoluminescence excitation (PLE) study.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
6
Spina, Carla. "Zinc oxide semiconducting nanocrystals : scaffolds for intrinsic and extrinsic defects." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115869.
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As a material whose applications are many and growing, zinc oxide still remains a complex system whose photoluminescent (PL), structural, electrical, and photocatalytic properties have not been fundamentally understood. The luminescent properties of zinc oxide (ZnO) nanocrystals (NCs) are very sensitive to crystal structure, and defect states in zinc oxide, which in turn is very sensitive to preparation methods, post-synthesis workup, and thermal treatments. Understanding and managing this rich defect chemistry is critical to controlling ZnO properties. As the surface-to-volume ratio of ZnO increases as materials enter the quantum regime, the surface defects play a stronger role. The exact role of the defect states and their contribution to the physical and chemical properties of ZnO has been studies in great lengths yet still remains controversial.
7
Dai, Xuemin, and 戴學敏. "Experimental and theoretical studies of defects related emissions in ZnO crystals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B4163388X.
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Dai, Xuemin. "Experimental and theoretical studies of defects related emissions in ZnO crystals." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B4163388X.
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Sun, Wei. "Defect Behaviors in Zinc Oxide and Zinc Titanates Ceramics from First Principles Computer Simulations." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955093/.
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ZnO and ZnO-TiO2 ceramics have intriguing electronic and mechanical properties and find applications in many fields. Many of these properties and applications rely on the understanding of defects and defect processes in these oxides as these defects control the electronic, catalytic and mechanical behaviors. The goal of this dissertation is to systematically study the defects and defects behaviors in Wurtzite ZnO and Ilmenite ZnTiO3 by using first principles calculations and classical simulations employing empirical potentials. Firstly, the behavior of intrinsic and extrinsic point defects in ZnO and ZnTiO3 ceramics were investigated. Secondly, the effect of different surface absorbents and surface defects on the workfunction of ZnO were studied using DFT calculations. The results show that increasing the surface coverage of hydrocarbons decreased the workfunction. Lastly, the stacking fault behaviors on ilmenite ZnTiO3 were investigated by calculating the Generalized Stacking Fault (GSF) energies using density functional theory based first principles calculations and classical calculations employing effective partial charge inter-atomic potentials. The gamma-surfaces of two low energy surfaces, (110) and (104), of ZnTiO3 were fully mapped and, together with other analysis such as ideal shear stress calculations.
10
蘇振強 and Chun-keung So. "Defect study of zinc oxide bulk materials by positron lifetime spectroscopy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B39558691.
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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.
12
Ye, Ziran, and 叶自然. "Studies of oxygen implantation induced deep level defects in zinc oxide single crystal." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47153854.
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Zinc Oxide (ZnO)is a wide band gap semiconductor which has attracted great attention because of its wide applicability. In order to obtain semiconductor devices with stable and reproducible properties further study of deep level defects is essential. DLTS (Deep level Transient Spectroscopy) is a direct and straightforward techniqueto determine the energy level of the deep level defects. Other information such as activation energy and capture cross section of the defect can also be obtained through this method. In our study ZnO single crystal samples were implanted by oxygen with the energy of 150keV. After the pretreatment of hydrogen peroxide, Schottky contacts were fabricated with Au
film deposited by thermal evaporation.
Deep level defects were studied by deep level transient spectroscopy (DLTS). Single peak spectra were observed in the as-implanted sample and samples anneal at 350oC, 650oC and 750oC with the corresponding activation energy decreasing with the annealing temperature from ~0.29eV as found in theas-implanted sample. Three peaks were identified in the DLTS spectra of the 900oC sample, with the activation energies of 0.11eV, 0.16eV and 0.37eV respectively.After analysis in detail we found some peaks in the DLTS spectra were the combination of two other peaks, dominated in different temperature range. The thermal evolutions of the deep levels up to the temperature of 1200oC were also investigated.published_or_final_version
Physics
Master
Master of Philosophy
13
Lu, Xiaohong, and 吕小红. "Deep level transient spectroscopic study of intrinsic defects in particle-irradiated ZnO single crystal materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47869914.
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Zinc oxide (ZnO), as a Ⅱ-Ⅵ compound semiconductor with a wide direct band gap, has attracted great attention from the worldwide researchers for its potential application in the fields of spintronics and optoelectronics. At present research about the defects in ZnO and ZnO-based materials is still far from complete. The deep level defects in melted grown ZnO single crystal induced by helium ions implantation and electron irradiation, as well as their thermal evolution, were studied in this research using the technique of deep level transient spectroscopy (DLTS) and photoluminescence (PL).
DLTS results indicated that, besides E3 (????~0.28 ????) trap which was widely observed in the as-grown ZnO samples, the deep level with ????~0.92 ???? was also indentified in the helium-implanted ZnO samples, which was introduced by the ion implantation and tentatively assigned to be the oxygen vacancy (VO). This deep level was removed after 350 oC annealing in argon gas. Annealing at 350 oC also brought along a new deep level with ????~0.66???? into helium-implanted samples which could be annealed out by 650 oC annealing in argon gas. The electron irradiation induced a deep level with ????~0.59 ???? into ZnO, which was probably associated with the singly charged state of VO. This deep level also tended to be removed at 350 oC annealing in argon gas. The PL spectra revealed that both helium implantation and electron irradiation could improve the bound-exciton peak. Helium implantation also introduced defects emission at 1.90 eV , which was the red luminescence band, into the ZnO single crystal materials. This red luminescence band peak might be associated with DAP recombination. Electron irradiation might restrain the green luminescence in ZnO single crystal. The fine structures could disappear as the measurement temperature increased, leaving the green luminescence band only.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
14
Ding, Guangwei, and 丁光炜. "Deep level transient spectroscopic study of nitrogen-implanted ZnO single crystal." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45541590.
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Zhu, Congyong. "Deep level defects study of arsenic implanted ZnO single crystal." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B40987759.
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To, Chun-kit, and 杜俊傑. "Defect studies of single crystal and thin film zinc oxide by positron annihilation spectroscopy and cathodoluminescence." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B4608955X.
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Zhu, Congyong, and 朱從佣. "Deep level defects study of arsenic implanted ZnO single crystal." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40987759.
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Herklotz, Frank. "Hydrogen-related defects in ZnO and TiO2." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-83311.
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Hydrogen-related defects in single-crystal ZnO and rutile TiO2 are investigated by means of infrared absorption, Raman scattering, photoluminescence and photoconductivity.
Four different defect centers in ZnO are considered: bond-centered hydrogen (HBC ), hydrogen bound within the oxygen vacancy (HO), hydrogen molecules, and a defect, which gives rise to a local vibrational mode at 3326 cm−1 .
The measurements identify HBC as a shallow donor with an ionization energy of 53 meV. The internal 1s → 2p transition of HBC is detected at 330 cm−1 in the Raman scattering and photoconductivity spectra. The decay of an exciton bound to HBC results in the photoluminescence line at 3360.1 ± 0.2 meV. The local vibrational mode of the O–H bond for bond-centered hydrogen has a frequency of 3611 cm−1 (H-I) and an effective charge of 0.28±0.03e. It is found that bond-centered hydrogen is unstable against annealing at 190 °C due to diffusion and trapping by other defects. The dominant sink is the hydrogen molecule.
It is demonstrated that the well-known I4 photoluminescence line at 3362.8 meV is due to the recombination of excitons bound to the HO donor.
The ionization energy of the HO donor is determined to be 47 meV. The 1s → 2pz (2pxy) electronic transition of HO is detected at 265 cm−1 in photoconductivity spectra. The formation of HO occurs via trapping of HBC at vacancies left by out-diffusing oxygen.
It is shown that sub-band gap illumination leads to an intensity reduction of the O–H local vibrational mode at 3326 cm−1 and the appearance of a previously unreported infrared absorption line at 3358 cm−1. The signals are identified as stretch modes of an O–H bond associated with the same defect in different charge states. The measurements indicate that this defect has a deep level in the band gap of ZnO at roughly Ec − 1.7 eV. Additionally, results on the thermal stability, uniaxial stress response, and temperature dependence of the transition rates between the two charge states of this defect are presented.
Interstitial hydrogen in rutile TiO2 is studied by infrared absorption. It is shown that the defect is a shallow donor with an ionization energy of 10 meV. The absorption lines at about 3290 cm−1 consists of local vibrational modes due to the neutral and the positive charge states of the donor with relative intensities depending on the measurement conditions. In the neutral charge state, the defect reveals two modes at 3288.3 and 3292 cm−1 (10 K), whereas the positive charge state has a vibrational mode at 3287.4 cm−1. An unknown hydrogen complex was found to contribute to the 3288 cm−1 feature.
19
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.
20
Ho, Lok-ping, and 何樂平. "Laplace transform deep level transient spectroscopic study on PLD grown ZnO." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2015. http://hdl.handle.net/10722/211117.
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The fundamental physics and techniques employed in Laplace transform deep level transient spectroscopy (L-DLTS) are reviewed. A Laplace-DLTS system has been constructed. The high resolving power of this system has been demonstrated experimentally.
The L-DLTS system was applied to characterize the defects in undoped n-type ZnO thin film grown by the pulsed laser deposition (PLD) method. A 0.3 eV deep trap has been identified. The formations of Ec-0.39eV and Ec-0.20eVcan be enhanced when the sample surface is seriously damaged by high temperature annealing.AnEc-0.25eV trap is identified in the freshly grown samples, but would disappear after the storage of 3 months.
Copper doped n-type ZnO thin film samples with low carrier concentration (n~〖10〗^16 〖cm〗^(-3)) were investigated by using both conventional and Laplace DLTS techniques. Positive DLTS signal peaks were detected that are suspected to be contributed by the minority carrier (hole carrier) emission. A physics model involving the inversion layer of a metal-insulator-semiconductor contact has been invoked to interpret the hole carrier concentration existing near the metal-semiconductor interface. Expression for the defect concentration is determined as a function of the temperature of DLTS peaks. AnEv+0.6eV defect with high concentration (N_T~〖10〗^17 〖cm〗^(-3)) was detected. The concentration of Ev+0.6eVcan be enhanced when the annealing temperature was increased from 750 to 900 degree C.published_or_final_version
Physics
Master
Master of Philosophy
21
Maller, Robert. "Defects and dopants in zinc oxide : a study of the optoelectronic properties of thin films prepared by spray pyrolysis." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/43373.
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Interest in transparent conducting oxides (TCOs) has intensified over the past decade, driven by the requirement to find a suitable replacement to indium tin oxide (ITO). Of the many possible candidates identified, zinc oxide (ZnO) was selected owing to its favourable optical properties, abundance, low toxicity and chemical stability. This thesis is directed towards finding low cost routes to producing transparent conducting ZnO thin films that could be utilised in a range of current and emerging optoelectronic devices. The spray pyrolysis technique is demonstrated as a highly appropriate low cost, large area deposition route to produce ZnO thin films. The necessity for, and the construction of, an automated rig for the deposition process is detailed. Excellent reproducibility is demonstrated compared with manual deposition. The structural, electrical and optical properties of native and doped ZnO are examined with the overall aim to optimise performance for TCO applications. The novel, AC Hall effect technique is employed to study the factors controlling charge carrier concentration and charge mobility across the a wide doping range, including in previously unexplored regions such as in the undoped and low doping regimes. Investigations into the optimal crystal structure for the greatest charge carrier concentration and charge mobility are made and links between the degree of (002) texturing and charge mobility suggested. Further studies into the position of Al, Ga and In dopants in the crystalline lattice show that the ionic radius plays a key role in the solubility of the dopant in the lattice. Ingress and egress of the zinc vacancy (VZn), and emergence of the hybrid dopant substitution/zinc vacancy (XZnVZn where X = Al, Ga, In) defects are suggested as likely candidate to explain observed electronic behaviour. Finally, the effect of annealing ZnO films is studied, and the necessity for Zn-rich films for TCO applications determined. Annealing in oxygen poor environments is shown to greatly reduce resistivity of films, with VZn defects suggested to be the main contributor to this effect. The stability of electronic improvements following annealing is presented; no observable degradation in performance is seen subsequent to 180 days storage in ambient conditions.
22
Mosbacker, Howard L. IV. "Control of Electrical Transport Mechanisms At Metal-Zinc Oxide Interfaces By Subsurface Defect Engineering With Remote Plasma Treatment." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204733572.
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Schmidt, Florian, Stefan Müller, Wenckstern Holger von, Gabriele Benndorf, Rainer Pickenhain, and Marius Grundmann. "Impact of strain on electronic defects in (Mg,Zn)O thin films." American Institute of Physics, 2014. https://ul.qucosa.de/id/qucosa%3A31192.
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We have investigated the impact of strain on the incorporation and the properties of extended and
point defects in (Mg,Zn)O thin films by means of photoluminescence, X-ray diffraction, deep-level
transient spectroscopy (DLTS), and deep-level optical spectroscopy. The recombination line Y2,
previously detected in ZnO thin films grown on an Al-doped ZnO buffer layer and attributed to tensile
strain, was exclusively found in (Mg,Zn)O samples being under tensile strain and is absent in
relaxed or compressively strained thin films. Furthermore a structural defect E3′ can be detected
via DLTS measurements and is only incorporated in tensile strained samples. Finally it is shown
that the omnipresent deep-level E3 in ZnO can only be optically recharged in relaxed ZnO samples.
24
Gao, Hantian. "Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1618838504594148.
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Cauduro, André Luís Fernandes. "Síntese, fotoluminescência e caracterização elétrica de nanoestruturas de ZnO." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/54881.
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Nanofios semicondutores de óxido metálico apresentam enorme potencial em aplicações de nano-sensoriamento de diferentes gases e substâncias químicas e biológicas, bem como na aplicação a detectores UV-visível. Neste trabalho, desenvolvemos e aperfeiçoamos a síntese de nanofios de ZnO em substratos de safira (001), silício (111) e silício (100) sob diferentes concentrações de oxigênio usando o processo de transporte de vapor-liquido-sólido (VLS). No presente trabalho, investigamos a influência da concentração de oxigênio no crescimento de nanofios de ZnO por Espectroscopia de Fotoluminescência a temperatura variável com a finalidade de estudo da mudança na concentração de defeitos. Apresentamos, ainda, caracterizações elétricas (IxV e Ixt) de nanoestruturas de ZnO sob diferentes pressões com o objetivo de estudar os defeitos envolvidos nos processos de transportes eletrônicos. Por último, propomos o desenvolvimento de micro-contatos através da técnica de microfeixe iônico e através de nanolitografia por feixe de elétrons com a finalidade de aplicações a sensores químicos, gasosos e fotodetectores.Metal oxide nanowires semiconductors have enormous potential in high-sensitive, fast and selective sensing applications. It may be used to selectively detect different gases, chemical and biological substances and also in UV-visible photodetectors. The described processes involve the synthesis as well as the characterization of ZnO nanowires grown on sapphire (001), silicon (100) e silicon (111) substrates by the Vapor-liquid-solid transport method. In the present work, we describe the influence of oxygen concentration introduced in the growth step measured by photoluminescence at variable temperature to demonstrate the change in defect levels emission (DLE). Furthermore, we have shown electrical characterization (IxV and Ixt) in order to study the ambient effect for transport mechanisms in ZnO nanowires. We also report the development of crucial steps in the fabrication for an upcoming ZnO nanowire sensor device (gas, chemical and photodetector) using lithography techniques such as ion micro-beam and electron beam with the purpose of fabricating metallic micro-pads.
26
Doutt, Daniel R. "THE ROLE OF NATIVE POINT DEFECTS AND SURFACE CHEMICAL REACTIONS IN THE FORMATION OF SCHOTTKY BARRIERS AND HIGH N-TYPE DOPING IN ZINC OXIDE." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366199639.
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Zhang, Zhichun. "Process Dependence of Defects and Dopants in Wide Band Gap Semiconductor and Oxides." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366107518.
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Önsten, Anneli. "Surface Reactivity and Electronic Structure of Metal Oxides." Doctoral thesis, KTH, Materialfysik, MF, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33667.
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The foci of this thesis are the metal oxides Cu2O, ZnO and Fe3O4 and their interaction with water and sulfur dioxide (SO2). The intention is to study SO2-induced atmospheric corrosion on a molecular level. All studies are based on photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM) measurements. The band structure of Cu2O in the Γ-M direction has been probed by angle-resolved PES (ARPES). It reveals a more detailed picture of the bulk band structure than earlier data and gives the first experimental evidence of a dispersive hybridized Cu 3d-Cu 4s state. The experimental data is compared to band structure calculations. The structure of clean metal oxide surfaces and impact of sample preparation have been studied. Oxygen vacancies can form a (√3x√3)R30° reconstruction on Cu2O(111). Oxygen atoms adjacent to copper vacancies, steps or kinks are shown to be adsorption sites for both water and SO2. Annealing temperature influences the defect density and hydrogen content in ZnO, which can have large impact on the surface properties of ZnO(0001). Water is shown to adsorb dissociatively on ZnO(0001) and partly dissociatively on Cu2O(111). The dissociation occurs at undercoordinated oxygen sites on both surfaces. Water stays adsorbed on ZnO(0001) at room temperature but on Cu2O(111), all water has desorbed at 210 K. SO2 interacts with one or two undercoordinated O-sites on all studied oxide surfaces forming SO3 or SO4 species respectively. SO4 on Fe3O4(100) follows the (√2x√2)R45° reconstruction. On Cu2O(111) and ZnO(0001), SO2 adsorbs on defect sites. An SO3 to SO4 transition is observed on Cu2O(111) when heating an SO3 adsorbate layer from 150 K to 280K. Coadsorption of water and SO2 on ZnO(0001) and Fe3O4(100) has been studied briefly. Water blocks SO2 adsorption sites on ZnO(0001). On Fe3O4(100) and on one type of reduced ZnO(0001) sample, SO2 dissociation to atomic sulfur or sulfide occurs to a higher extent on water exposed surfaces than on clean surfaces. Water thus appears to increase the charge density on some surfaces. Further studies are needed to reveal the cause of this unexpected effect.QC 20110516
29
Pascua, Arcusin Leandro Enrique [Verfasser]. "Exploring the Luminescence Characteristics of Zinc Oxide Thin Films: The Role of Defects, Impurities and Metal Ad Particles : A Scanning Tunneling Microscopy Study / Leandro Enrique Pascua Arcusin." Berlin : Freie Universität Berlin, 2015. http://d-nb.info/1076775667/34.
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Schmidt, Florian. "Raumladungszonenspektroskopische Methoden zur Charakterisierung von weitbandlückigen Halbleitern." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-158772.
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Die Arbeit befasst sich mit der Untersuchung von weitbandlückigen Halbleitern über raumladungszonenspektroskopische Methoden. Dabei liegt der Schwerpunkt auf der Detektion von elektronisch und optisch aktiven Defektzuständen in solchen Materialien. Die Experimente wurden exemplarisch an dem II-VI Halbleiter Zinkoxid (ZnO) durchgeführt, welcher inform von Volumenkristallen, Mikronadeln und Dünnfilmen zur Verfügung stand. Raumladungszonen wurden über Schottky-Kontakte realisiert. Nach einer Einführung in die Theorie der Raumladungszonenspektroskopie wird ein Überblick über Defekte in verschiedenartig gezüchteten ZnO gegeben. Dazu werden die Standardverfahren Strom-Spannungs-Messung, Kapazitäts-Spannungs-Messung, Thermische Admittanz- Spektroskopie (TAS) und Deep Level Transient Spectroscopy (DLTS) verwendet. Ergänzend wurden die auf weitbandlückige Halbleiter ausgelegten Verfahren Low Rate Deep Level Transient Spectroscopy (LR-DLTS) und Deep Level Optical Spectroscopy (DLOS) eingesetzt, mit welchen es möglich ist Defektzustände in der gesamten Bandlücke von ZnO nachzuweisen. Für die untersuchten Störstellenniveaus konnten somit die thermische Aktivierungsenergie, Einfangquerschnitte freier Ladungsträger und Photoionisationsquerschnitte bestimmt werden.
Typischerweise werden tiefe Defekte durch die Bestrahlung mit hochenergetischen Protonen erzeugt. Derartige Behandlungen wurden an binären ZnO- und ternären (Mg,Zn)ODünnfilmen durchgeführt, wobei die Generationsrate eines Defektes über Variation der verwendeten Strahlungsdosis bestimmt wurde. Ionenimplantationen spielen eine große Rolle im Herstellungsprozess von Bauelementen, sind jedoch für ZnO nicht etabliert. Die Auswirkung der Implantation von inerten Argon-Ionen, sowie die nachträgliche thermische Behandlung auf die Konzentration intrinsischer Defekte wurde untersucht. Zink- und Sauerstoff-Implantationen bewirken, neben der Generation von Defekten, eine lokale Änderung der Stöchiometrie. Durch einen Vergleich der Defektkonzentrationen nach Zn-, O-, Ne- und Ar-Implantation können Rückschlüsse auf die chemische Natur intrinsischer Defekte geschlossen werden.
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Mbulanga, Crispin Munyelele. "Defect-related photoluminescence of zinc oxide nanorods." Thesis, Nelson Mandela Metropolitan University, 2015. http://hdl.handle.net/10948/10318.
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In this dissertation, Zinc oxide (ZnO) nanorods grown by a two-step chemical bath deposition method on Si substrate is characterized. Research was conducted on ZnO nanorods for the understanding of their optical properties at room temperature (RT), with the emphasis on the visible luminescence. To this end, controlled thermal treatments of as-grown ZnO nanorods were conducted under different conditions, such as annealing time and environment, at atmospheric pressure. Results related to the following studies are reported: an investigation of the structure of ZnO nanorods, an analysis of the chemical composition of the surface, an investigation of the surface stoichiometry of the rods, and a study of defect-related photoluminescence of ZnO nanorods upon thermal treatment in different ambients.To achieve this, the samples were investigated by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and room temperature (RT) photoluminescence Spectroscopy (PL). As-grown ZnO nanorods exhibit a hexagonal shape and have the wurtzite structure; they have, respectively, an average length and diameter of ~900 nm and ~50 nm, and most of the rods are perpendicular to the substrate. The main extrinsic species found in as-grown nanostructures are C, H, F, S, and Cl. ToF-SIMS and XPS confirmed the presence of H related-defects, and the oxygen 1 S XPS peak at 531.5 eV is therefore assigned to oxygen bound to H-related defects. Based on stoichiometry studies, it is found that the near surface regions of as-grown ZnO nanorods (2 to 10 monolayers) are rich in Zn. The RT luminescence of as-grown ZnO nanorods exhibits a near band edge emission centered at ~379.5 nm and deep level emission extending from ~450 nm to ~850 nm. When these nanorods are thermally treated at high temperatures (>850 oC), it is found that even though their crystalline quality is preserved, their morphology is significantly affected, regardless of annealing ambient. Furthermore, in the near surface regions of annealed ZnO nanorods it is found that the Zn/O stoichiometric ratios deviate from unity. Specifically, oxygen vacancies form within the first 100 nm from the sample surface. Further from the surface, the material is deficient in Zn. It is deduced from XPS and AES that the ambient affects the activation rate of intrinsic defects. Furthermore, the only extrinsic defects that are affected by thermal treatment are found to be H-related defects. At high annealing temperatures (300 oC to ~700 oC), H-related defects are removed, and this removal process is found to affect significantly the RT luminescence properties of ZnO nanorods. Specifically, hydrogen passivates vacancy-related defects, depending on the thermal treatment. PL spectroscopy is used to follow this passivation effect as a function of annealing temperature, which causes an initial quenching followed by an enhancement of the green and the red luminescence, regardless of the ambient. Finally, the green luminescence that arises following annealing above ~800 oC is assigned to Zn vacancy-related defects, while the red luminescence that dominates the visible band of ZnO nanorods upon annealing between 400 oC and 600 oC is suggested to be due to oxygen vacancy-related defects.
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So, Chun-keung. "Defect study of zinc oxide bulk materials by positron lifetime spectroscopy." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/HKUTO/record/B39558691.
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Williamson, Andrew. "Carrier dynamics, persistent photoconductivity and defect chemistry at zinc oxide photoanodes." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/carrier-dynamics-persistent-photoconductivity-and-defect-chemistry-at-zinc-oxide-photoanodes(ec59e44c-0f17-40e5-ab34-871afbea0ea9).html.
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Zinc oxide (ZnO) is a promising photoanode material which has been used in quantum dot-based depleted heterojunction solar cells. The specific influence of the defect chemistry of ZnO on its n-type conductivity remains a focus for research. This thesis presents results from a series of near-ambient pressure (NAP) XPS experiments (at The University of Manchester, UK), used to characterise surface adsorption of O2 and H2O on ZnO(10-10) surfaces in high pressure environments. Water dosing is shown to lead to surface hydroxylation and a change in the surface band bending consistent with an increase in the surface conductivity. Oxygen dosing is also observed to lead to the formation of surface species on the ZnO surface, revealing that ZnO is prone to hydroxylation even in oxygen-rich environments. The role of surface OH on influencing the transient surface photovoltage (SPV) of the ZnO(10-10) surface is probed through a series of time-resolved, pump-probe XPS experiments (at SOLEIL synchrotron, France). It is shown that increasing the degree of surface hydroxylation leads to a decrease in surface band bending, leading to longer-lived transient SPV. Other factors influencing the SPV dynamics are explored, such as the role of the oxygen vacancy concentration. The transient SPV decay lifetime is shown to increase with increasing oxygen vacancy concentration, consistent with the presence of persistent photoconductivity (PPC) in ZnO, mediated by oxygen vacancy-related hole traps. The influence of the concentration of thermally excited carriers in ZnO on the surface band bending is also described, showing that the equilibrium band bending and the surface photovoltage are both reduced at low temperature. It is shown that thermal excitation of carriers from the valence band of ZnO and from neutral oxygen vacancies have negligible influence on the magnitude of equilibrium band bending at the surface. The energy regime consistent with the observed temperature dependence is also consistent with a perturbed-host state 0.2 eV below the conduction band minimum. This meta-stable state is associated with doubly-ionised oxygen vacancies, that mediate the PPC in ZnO. However this does not rule out the contribution from other shallow donor levels such as those associated with hydrogen impurities. The influence of hydrogen on the SPV dynamics in ZnO is explored, through angle-resolved photoemission spectroscopy (ARPES) after implanting hydrogen atoms into the ZnO surface. H implantation is shown to lead to the formation of a 2D electron gas (2DEG) at the surface, consistent with an increase in conductivity at the surface large enough to change the nature of the space-charge region at the ZnO surface from depletion to accumulation.
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Rezaei, Seyed Emad. "Defect Engineering: Novel Strengthening Mechanism for Low- Dimensional Zinc Oxide Nanostructures." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1532902032338622.
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Foster, Geoffrey M. "DEFECT AND METAL OXIDE CONTROL OF SCHOTTKY BARRIERS AND CHARGE TRANSPORT AT ZINC OXIDE INTERFACES." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524050368601169.
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Tecklenburg, Stefanie [Verfasser], Andreas [Gutachter] Erbe, and Anjana [Gutachter] Devi. "Defect formation and evolution in zinc oxide : from semiconductors to corrosion / Stefanie Tecklenburg ; Gutachter: Andreas Erbe, Anjana Devi ; Fakultät für Chemie und Biochemie." Bochum : Ruhr-Universität Bochum, 2021. http://d-nb.info/1230631216/34.
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Zhang, Miao. "Defects in ZnO nanoparticles obtained by gas-phase syntheses." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066259.
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L’attribution des signatures spectrales liées aux défauts dans l’oxyde de zinc fait encore l’objet de controverses. Ceci est probablement dû à la grande variété de défauts possibles, à l’incertitude de leur niveau d’énergie ainsi que leur énergie de formation dans la bande interdite. De plus, l’imprécision concernant les conditions de mesures et la possible présence d’impuretés inhérentes à certaines méthodes de synthèse peuvent souvent mener à des interprétations erronées. Le but de ce travail de thèse est donc d’identifier les défauts intrinsèques naturellement présents dans du ZnO fraîchement préparé ou bien formés via différents types de traitements post-synthèse. Pour atteindre ce but, notre stratégie fut (i) de préparer des nanoparticules modèles de ZnO en utilisant deux types de synthèses en phase vapeur (Combustion et CVS) (ii) de combiner des mesures in situ de photoluminescence (PL) et de RPE, également associées à des spectroscopies complémentaires (Raman, UV visible, FTIR) de façon à révéler, attribuer les défauts et discuter leur comportement selon les conditions de synthèses et de traitements post-synthèse et (iii) de révéler la réactivité des surfaces défectueuses de nos échantillons de ZnO en étudiant leur interaction avec des molécules d’eau ou de 2-méthyl-3-butyn-2-ol (MBOH). Nous avons ainsi observé que VO2+ et Zni+ sont les défauts natifs prédominants dans tous les échantillons fraîchement préparés de ZnO, dans des quantités relatives dépendant de la pression partielle d’oxygène utilisée lors de la synthèse. Les lacunes neutres d’oxygène (VO0) ont également été détectées dans le cas des préparations effectuées dans des conditions particulièrement riches en zinc. VO+ peut se former dans le ZnO smoke après post-traitement (recuit sous vide ou sous vapeur de zinc), la formation d’électrons associée participant à la réduction de Zni+ en Zn0. Au contraire, calciner sous O2 mène à des processus opposés, voire, sous excès d’O2, à la formation de défaut de type Oi. La dissociation de l’eau sur des surfaces préalablement calcinées sous vide mène au remplissage de VO+ et à la réduction de Zn2+ en Zn+. Des tests catalytiques de conversion du MBOH ont montré que de tels processus redox, contrôlés par les conditions de prétraitement, affectent la réactivité de surface de nos matériauxBy far, the assignment of defects-related spectroscopic features of zinc oxide is still a matter of great controversy. This is probably due to the variety of possible defects in ZnO as well as to their still uncertain formation energies and positions within the band gap. Uncontrolled measurement conditions and impurities related to some synthesis methods can additionally mislead interpretations. The aim of this work is to identify the intrinsic native defects in pure ZnO or formed upon different kind of post-synthesis treatments. To fulfill this goal our strategy was to: i) prepare model zinc oxide nanoparticles using two different vapor-phase synthesis techniques (Combustion and CVS) ii) identify, assign and discuss the occurrence of the defects in line with the synthesis and post treatments conditions by combining in situ PL and EPR measurements together with other complementary spectroscopies (Raman, UV vis, FTIR) and iii) reveal the surface reactivity of defective ZnO samples by studying the interaction with water or 2-methyl-3-butyn-2-ol (MBOH). We observed that in all as-synthesized ZnO samples VO2+ and Zni+ are the predominant native defects with relative amounts depending on the partial pressure of oxygen used during the synthesis. Neutral oxygen vacancies (VO0) are additionally detected in samples prepared in conditions particularly rich in zinc. The formation of Vo+ is demonstrated in ZnO smoke upon post treatment (annealing in high vacuum or zinc vapor) while the associated electron release is shown to participate to the reduction of Zni+ into Zn0. On the contrary, annealing in oxygen leads to reverse processes while if used in an excess, to creation of Oi-related defects. Dissociation of water on vacuum annealed surface leads to the filling up of VO+, and reduction of Zn2+ into Zn+. Such redox processes controlled by the pretreatment conditions affect the surface reactivity through the change of the acid base balance, as revealed by MBOH conversion catalytic tests
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Schmidt, Matthias [Verfasser], Wenckstern Holger [Akademischer Betreuer] von, Rainer [Akademischer Betreuer] Pickenhain, Marius [Akademischer Betreuer] Grundmann, Marius [Gutachter] Grundmann, Gerhard [Akademischer Betreuer] Brauer, and Stephen J. [Gutachter] Pearton. "Space Charge Spectroscopy applied to Defect Studies in Ion-Implanted Zinc Oxide Thin Films / Matthias Schmidt ; Gutachter: Marius Grundmann, Stephen J. Pearton ; Holger von Wenckstern, Rainer Pickenhain, Marius Grundmann, Gerhard Brauer." Leipzig : Universitätsbibliothek Leipzig, 2012. http://d-nb.info/1238021115/34.
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Perrin, Kévin. "Etude des phénomènes de diffusion à l'état solide impliqués dans les réactions hétérogènes gaz-solide : application à la sulfuration de l'oxyde de zinc." Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCK064/document.
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Les phénomènes de transformation de phases avec interface réactionnelle mobile interviennent dans une grande variété de réactions chimiques et d’applications. Les réactions de sulfuration d'oxydes métalliques mènent par exemple à la formation de phases sulfures dans des applications concernant la purification de gaz ou la préparation de catalyseurs. Ces réactions impliquent entre autres des phénomènes de diffusion des espèces réactives à l’état solide (sous forme atomique ou ionique) à travers la couche de produit formée lors de la réaction (phase oxyde, sulfure ou métal). Dans de nombreux cas, les phénomènes de diffusion à l’état solide ont un impact direct sur les mécanismes ainsi que sur la cinétique globale des réactions, et déterminent le sens de croissance des phases formées. Cette thèse a pour objectif d’apporter une meilleure compréhension des phénomènes de diffusion d’espèces réactives à l’état solide impliqués dans les réactions hétérogènes gaz-solide. En particulier, cette étude porte sur le cas de la réaction de sulfuration de l’oxyde de zinc par H2S menant à la formation de ZnS. L’influence de la structure cristalline, de la présence d’impuretés et/ou de défauts ponctuels natifs ou extrinsèques et l’impact des phénomènes de diffusion sur la cinétique réactionnelle globale ont été étudiés. La stratégie de recherche proposée comporte un volet expérimental via la synthèse et la caractérisation de matériaux dopés, et l’étude de la cinétique de la réaction de sulfuration par thermogravimétrie sous atmosphère réactive. Le travail expérimental a été complété par une approche théorique par dynamique moléculaire permettant la détermination de coefficients de diffusion dans différents systèmes (ZnO et ZnS), mono/polycristallins, et avec/sans présence de dopants. La détermination des processus de diffusion et des paramètres qui la gouvernent permet d’aboutir, in fine, à une meilleure compréhension des réactions hétérogènes solide-gazPhase transition phenomena involving the mobility of the reaction interface are involved in a wide variety of chemical reactions and applications. A good example is the sulfidation reaction experienced by the metal oxide-based materials used in the framework of gas purification or catalysts preparation applications. These reactions involve solid-state diffusion phenomena of the reactive species (atomic or ionic form) through the layer of product formed during the reaction (oxide, sulfide, or metal phase). In many cases, solid-state diffusion has a direct impact on the reaction mechanisms while determining the growth direction of the formed phases, as well as the overall kinetics of the reactions. This PhD-thesis work aims at providing a better understanding of the solid-state diffusion phenomena of reactive species involved in gas-solid heterogeneous reactions. In particular, the study is focused on zinc oxide sulfidation reaction with H2S, in which the influence of the crystal structure of solids, the presence of impurities and / or native or extrinsic point defects, and the impact of diffusion phenomena on the overall reaction kinetics were evaluated. The research strategy relies on a first experimental approach via the synthesis and characterizations of doped materials, followed by the determination of their sulfidation reaction kinetics by thermogravimetry under reactive atmosphere. The experimental work was combined to a theoretical approach based on Molecular Dynamics, which allows the determination of diffusion coefficients in different systems (ZnO and ZnS), mono/polycrystalline, and with/without presence of doping elements. Knowledge of the diffusion processes and of key parameters involved leads to a better understanding of solid-gas heterogeneous reactions
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Skorupa, Wolfgang, and Gerhard Brauer. "HeT-SiC-05International Topical Workshop on Heteroepitaxy of 3C-SiC on Silicon and its Application to Sensor DevicesApril 26 to May 1, 2005,Hotel Erbgericht Krippen / Germany- Selected Contributions -." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28591.
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This report collects selected outstanding scientific and technological results obtained within the frame of the European project "FLASiC" (Flash LAmp Supported Deposition of 3C-SiC) but also other work performed in adjacent fields. Goal of the project was the production of large-area epitaxial 3C-SiC layers grown on Si, where in an early stage of SiC deposition the SiC/Si interface is rigorously improved by energetic electromagnetic radiation from purpose-built flash lamp equipment developed at Forschungszentrum Rossendorf. Background of this work is the challenging task for areas like microelectronics, biotechnology, or biomedicine to meet the growing demands for high-quality electronic sensors to work at high temperatures and under extreme environmental conditions. First results in continuation of the project work – for example, the deposition of the topical semiconductor material zinc oxide (ZnO) on epitaxial 3C-SiC/Si layers – are reported too.
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Skorupa, Wolfgang, and Gerhard Brauer. "HeT-SiC-05International Topical Workshop on Heteroepitaxy of 3C-SiC on Silicon and its Application to Sensor DevicesApril 26 to May 1, 2005,Hotel Erbgericht Krippen / Germany- Selected Contributions -." Forschungszentrum Rossendorf, 2005. https://hzdr.qucosa.de/id/qucosa%3A21685.
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This report collects selected outstanding scientific and technological results obtained within the frame of the European project "FLASiC" (Flash LAmp Supported Deposition of 3C-SiC) but also other work performed in adjacent fields. Goal of the project was the production of large-area epitaxial 3C-SiC layers grown on Si, where in an early stage of SiC deposition the SiC/Si interface is rigorously improved by energetic electromagnetic radiation from purpose-built flash lamp equipment developed at Forschungszentrum Rossendorf. Background of this work is the challenging task for areas like microelectronics, biotechnology, or biomedicine to meet the growing demands for high-quality electronic sensors to work at high temperatures and under extreme environmental conditions. First results in continuation of the project work – for example, the deposition of the topical semiconductor material zinc oxide (ZnO) on epitaxial 3C-SiC/Si layers – are reported too.
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Taïnoff, Dimitri. "Influence des défauts sur les propriétés optiques et électroniques des nanoparticules de ZnO." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00507281.
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L'objectif de cette étude est de mieux comprendre le rôle joué par les défauts dans les propriétés optiques et électroniques des nanostructures d'oxyde de zinc. Pour ce faire, nous avons synthétisé des nanoparticules d'oxyde de zinc de 6 à 18 nm de diamètres pouvant être considérées comme modèle en terme de stœchiométrie, de cristallinité et de qualité de surface par une méthode physique originale : la Low Energy Cluster Beam Deposition.La caractérisation optique des défauts présents dans les nanoparticules de ZnO a été faite grâce à l'analyse des spectres d'émission visible et UV à différentes températures [10K-300K]. En particulier la luminescence excitonique à 3,31 eV, qui est un sujet controversé, a été étudiée en comparant la luminescence excitonique d'échantillons structurés à différentes échelles (nanoparticules, microcristaux et monocristal). Les temps de déclins très rapides des défauts donneurs ont été étudiés par spectroscopie à décalage de fréquence au CELIA à Bordeaux révélant une dépendance en fonction de la taille des NPs du type Giant Oscillator Strenght.Les propriétés de transport électronique des couches minces de NPs, naturellement dopées n, ont été caractérisées grâce à des expériences σ(T). Différents scénarios sont proposés pour expliquer les résultats des expériences de conductivité, et discutés en fonction des propriétés optiques des couches et de leur morphologie. En particulier, il est montré que la surface des NPs, très réactive, influence fortement le transport, ce qui laisse entrevoir la possibilité d'utiliser ces films nanostructurés comme capteurs de gaz.
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Brochen, Stéphane. "Propriétés électriques du ZnO monocristallin." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00872067.
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L'oxyde de zinc ZnO, est un semiconducteur II-VI très prometteur pour les applications en opto-électronique dans le domaine UV, notamment pour la réalisation de dispositifs électroluminescents (LED). Les potentialités majeures du ZnO pour ces applications résident notamment dans sa forte liaison excitonique (60 meV), sa large bande interdite directe (3.4 eV), la disponibilité de substrats massifs de grand diamètre ainsi que la possibilité de réaliser des croissances épitaxiales de très bonne qualité en couches minces ou nano structurées (nanofils). Néanmoins, le développement de ces applications est entravé par la difficulté de doper le matériau de type p. L'impureté permettant d'obtenir une conductivité électrique associée à des porteurs de charges positifs (trous), et donc la réalisation de jonctions pn à base de ZnO, n'a pas encore été réellement identifiée. C'est pourquoi une des étapes préliminaires et nécessaires à l'obtention d'un dopage de type p fiable et efficace, réside dans la compréhension du dopage résiduel de type n, ainsi que des phénomènes de compensation et de passivation qui sont mis en jeu au sein du matériau. La maîtrise de la nature des contacts (ohmique ou Schottky) sur différentes surfaces d'échantillons de ZnO nous a permis dans ce but de mettre en œuvre à la fois des mesures de transport (résistivité et effet Hall) et des mesures capacitives (capacité-tension C(V), Deep Level Transient Spectroscopy (DLTS) et Spectroscopie d'admittance).Dans un premier temps, nous avons donc cherché à comprendre de manière approfondie les propriétés électriques du ZnO massif. Nous avons ainsi étudié le rôle des défauts profonds et peu profonds sur la conductivité des échantillons, aux travers de différents échantillons massifs obtenus par synthèse hydrothermale ou par croissance chimique en phase vapeur. Nous avons également étudié l'impact de la température de recuits post-croissance, sur les propriétés de transport des échantillons. A la lumière des résultats obtenus sur le dopage résiduel de type n des échantillons de ZnO massifs, nous avons ensuite procédé à différents essais de dopage de type p du ZnO par implantation ionique d'azote et par diffusion en ampoule scellée d'arsenic. L'impureté azote a été choisie dans le cadre d'une substitution simple de l'oxygène qui devrait permettre de créer des niveaux accepteurs dans la bande interdite du ZnO. Nous avons également étudié l'impureté arsenic, qui selon un modèle théorique peut former un complexe qui permet d'obtenir un niveau accepteur plus proche de la bande de valence que le niveau. Outres les études réalisées sur les échantillons de ZnO massif et les essais de dopage de type p, nous avons également étudié les propriétés électriques d'échantillons de ZnO monocristallins sous forme de couches minces obtenues par croissance en phase vapeur d'organométalliques, dopées intentionnellement ou non. Les corrélations entres les mesures SIMS et C(V) nous ont permis notamment de mettre en évidence une diffusion et un rôle très importante de l'aluminium sur les propriétés électriques des couches minces de ZnO épitaxiées sur substrat saphir.Dans le cadre de cette thèse nous avons réussi à clarifier les mécanismes du dopage de type n, intentionnel ou non intentionnel, dans le ZnO monocristallin. Nous avons également identifié les impuretés et les paramètres de croissance importants permettant d'obtenir un dopage résiduel de type n le plus faible possible dans les couches épitaxiées. Cette maitrise du dopage résiduel de type n est une étape préliminaire indispensable aux études de dopage de type p car elle permet de minimiser la compensation des accepteurs introduits intentionnellement. Cette approche du dopage sur des couches minces de ZnO dont le dopage résiduel de type n est très faible apparait comme une voie très prometteuse pour surmonter les problèmes d'obtention du dopage de type p.
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Erhart, Paul. "Intrinsic Point Defects in Zinc Oxide: Modeling of Structural, Electronic, Thermodynamic and Kinetic Properties." Phd thesis, 2006. http://tuprints.ulb.tu-darmstadt.de/726/1/prim.pdf.
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The present dissertation deals with the modeling of zinc oxide on the atomic scale employing both quantum mechanical as well as atomistic methods. The first part describes quantum mechanical calculations based on density functional theory of intrinsic point defects in ZnO. To begin with, the geometric and electronic structure of vacancies and oxygen interstitials is explored. In equilibrium oxygen interstitials are found to adopt dumbbell and split interstitial configurations in positive and negative charge states, respectively. Semi-empirical self-interaction corrections allow to improve the agreement between the experimental and the calculated band structure significantly; errors due to the limited size of the supercells can be corrected by employing finite-size scaling. The effect of both band structure corrections and finite-size scaling on defect formation enthalpies and transition levels is explored. Finally, transition paths and barriers for the migration of zinc as well as oxygen vacancies and interstitials are determined. The results allow to interpret diffusion experiments and provide a consistent basis for developing models for device simulation. In the second part an interatomic potential for zinc oxide is derived. To this end, the Pontifix computer code is developed which allows to fit analytic bond-order potentials. The code is subsequently employed to obtain interatomic potentials for Zn-O, Zn-Zn, and O-O interactions. To demonstrate the applicability of the potentials, simulations on defect production by ion irradiation are carried out.
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(11181615), Xin Li Phuah. "Flash sintering of zinc oxide and the growth of its nanostructures." Thesis, 2021.
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Flash sintering was first demonstrated in 2010, where a ceramic green body was rapidly densified within seconds by applying an electric field during the heating process. The ultra-fast densification can occur as current abruptly flows through the material and self-heats by Joule heating. This process has potentials for large energy savings due to the reduction in furnace temperatures and shortened sintering time compared to conventional sintering. In addition, the ultra-high heating and cooling rates, along with the impact of electric field and current leads to the formation of unique non-equilibrium features in ceramics, which could greatly enhance their properties. Despite the potential of flash sintering, there are many challenges in moving this technique towards practical applications, such as the microstructure inhomogeneity and lack of understanding of the defects characteristics.
In this dissertation, flash sintering was performed on ZnO to investigate the influence of various electrical conditions on the microstructure and defects. Detailed characterization was performed on flash sintered ZnO with and without a controlled current ramp, and contrasting types of current (DC and AC). These parameters show significant impact on the gradient microstructure and defects, and provide a way to tailor the desired characteristics for a wide range of applications. On the other hand, flash sintering of ZnO performed with a high electric field and low current density resulted in the growth of nanostructures. These nanostructures are unique compared to other growth techniques as they contain high density basal-plane stacking faults, and exhibit ultraviolet excitonic emission and red emission at room temperature. The nanostructure growth mechanism was investigated by varying the current density limit and revealed the formation of liquid phases which allowed growth by the vapor-liquid-solid mechanism. These findings present a new exciting route for flash sintering to produce highly defective nanostructures for device applications with new functionalities.
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Schmidt, Matthias. "Space Charge Spectroscopy applied to Defect Studies in Ion-Implanted Zinc Oxide Thin Films." Doctoral thesis, 2011. https://ul.qucosa.de/id/qucosa%3A11364.
Full textAbstract:
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.
47
Erhart, Paul [Verfasser]. "Intrinsic point defects in zinc oxide : modeling of structural, electronic, thermodynamic and kinetic properties / vorgelegt von Paul Erhart." 2006. http://d-nb.info/981134432/34.
Full text
48
Herklotz, Frank. "Hydrogen-related defects in ZnO and TiO2." Doctoral thesis, 2011. https://tud.qucosa.de/id/qucosa%3A25888.
Full textAbstract:
Hydrogen-related defects in single-crystal ZnO and rutile TiO2 are investigated by means of infrared absorption, Raman scattering, photoluminescence and photoconductivity.
Four different defect centers in ZnO are considered: bond-centered hydrogen (HBC ), hydrogen bound within the oxygen vacancy (HO), hydrogen molecules, and a defect, which gives rise to a local vibrational mode at 3326 cm−1 .
The measurements identify HBC as a shallow donor with an ionization energy of 53 meV. The internal 1s → 2p transition of HBC is detected at 330 cm−1 in the Raman scattering and photoconductivity spectra. The decay of an exciton bound to HBC results in the photoluminescence line at 3360.1 ± 0.2 meV. The local vibrational mode of the O–H bond for bond-centered hydrogen has a frequency of 3611 cm−1 (H-I) and an effective charge of 0.28±0.03e. It is found that bond-centered hydrogen is unstable against annealing at 190 °C due to diffusion and trapping by other defects. The dominant sink is the hydrogen molecule.
It is demonstrated that the well-known I4 photoluminescence line at 3362.8 meV is due to the recombination of excitons bound to the HO donor.
The ionization energy of the HO donor is determined to be 47 meV. The 1s → 2pz (2pxy) electronic transition of HO is detected at 265 cm−1 in photoconductivity spectra. The formation of HO occurs via trapping of HBC at vacancies left by out-diffusing oxygen.
It is shown that sub-band gap illumination leads to an intensity reduction of the O–H local vibrational mode at 3326 cm−1 and the appearance of a previously unreported infrared absorption line at 3358 cm−1. The signals are identified as stretch modes of an O–H bond associated with the same defect in different charge states. The measurements indicate that this defect has a deep level in the band gap of ZnO at roughly Ec − 1.7 eV. Additionally, results on the thermal stability, uniaxial stress response, and temperature dependence of the transition rates between the two charge states of this defect are presented.
Interstitial hydrogen in rutile TiO2 is studied by infrared absorption. It is shown that the defect is a shallow donor with an ionization energy of 10 meV. The absorption lines at about 3290 cm−1 consists of local vibrational modes due to the neutral and the positive charge states of the donor with relative intensities depending on the measurement conditions. In the neutral charge state, the defect reveals two modes at 3288.3 and 3292 cm−1 (10 K), whereas the positive charge state has a vibrational mode at 3287.4 cm−1. An unknown hydrogen complex was found to contribute to the 3288 cm−1 feature.
49
Bhat, Soumya S. "First-Principles Studies of Point Defects and Phase Transformations in Materials." Thesis, 2014. http://hdl.handle.net/2005/3022.
Full textAbstract:
The functional and mechanical properties of a material are often determined by the defects in them. A thorough understanding of the relationship between the defects and the properties allows for tailoring a material’s properties into the desired combinations. Amongst the different classes of defects, experimental identification of point defects is typically difficult and indirect, usually requiring an ingenious combination of different techniques. In this context, first-principles calculations, complemented with experiments, offer insights into the formation of defects and their role in properties. This was demonstrated in this thesis through investigations on the effect of calcium vacancies on structure, vibrational and elastic properties hydroxyapatite (HAp), and oxygen vacancies on elastic properties of zinc oxide (ZnO) using first-principles calculations based on density functional theory (DFT). Our results confirm a considerable reduction in the elastic constants of HAp—the inorganic constituent of bone—due to Ca-deficiency, which was experimentally reported earlier. Elastic anisotropic behavior of stoichiometric and Ca-deficient HAp is analyzed, which will be useful in understanding the effects of crystal orientation in designing synthetic bone. Local structural stability of HAp and Ca-deficient HAp structures is assessed with full phonon dispersion studies and the specific signatures in the computed vibrational spectra for Ca deficiency in HAp can be utilized in experimental characterization of different types of defected HAp. In ZnO, formation energies of oxygen vacancies in different types of oxygen deficient structures are analyzed to ascertain their stability. Our results show considerable degradation of some of the elastic moduli due to the presence of such vacancies. Further, the charge state of the defect structure is found to influence the shear elastic constants. Evaluation of elastic anisotropy of stoichiometric and oxygen deficient ZnO indicates the significant anisotropy in elastic properties and stiff c-axis orientation.
The second part of the thesis deals with developing some understanding of the pressure-induced phase transformations (PIPT) in an inorganic material, titanium nitride (TiN), and in a metal-organic framework (MOF), erbium formate crystal. PIPT, which is a common phenomenon in many materials, is of great interest in materials science as the properties of the transformation product can diverge significantly from those of the parent phase. Hence, it is important to understand the pressure induced changes so to improve the component reliability and to enhance service life of materials used in high pressure applications. TiN undergoes PIPT from NaCl to CsCl structure. On the basis of our DFT calculations, we propose a new transformation path, which shows that the stress required for this transformation is substantially lower when it is deviatoric in nature than that under hydrostatic pressure. Local stability of the structure is assessed with phonon dispersion determined at different pressures, and we find that CsCl structure of TiN is expected to distort after the transformation. Further, we provide a quantitative comparison of electronic structure of TiN in NaCl structure with that of high pressure phase with implication to electrical conduction properties. Next, we investigate the PIPT associated with bond rearrangement in erbium formate framework. Phase transition pressure is estimated and the corresponding changes in bonding characteristics are analyzed. Estimated lattice constants for both the phases agree well with the earlier experimental results. While the transformation pressure of the framework is overestimated with respect to experiment, our calculations confirm PIPT, and thus provide a theoretical evidence for the experimental finding.
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Schmidt, Florian. "Raumladungszonenspektroskopische Methoden zur Charakterisierung von weitbandlückigen Halbleitern." Doctoral thesis, 2014. https://ul.qucosa.de/id/qucosa%3A13079.
Full textAbstract:
Die Arbeit befasst sich mit der Untersuchung von weitbandlückigen Halbleitern über raumladungszonenspektroskopische Methoden. Dabei liegt der Schwerpunkt auf der Detektion von elektronisch und optisch aktiven Defektzuständen in solchen Materialien. Die Experimente wurden exemplarisch an dem II-VI Halbleiter Zinkoxid (ZnO) durchgeführt, welcher inform von Volumenkristallen, Mikronadeln und Dünnfilmen zur Verfügung stand. Raumladungszonen wurden über Schottky-Kontakte realisiert. Nach einer Einführung in die Theorie der Raumladungszonenspektroskopie wird ein Überblick über Defekte in verschiedenartig gezüchteten ZnO gegeben. Dazu werden die Standardverfahren Strom-Spannungs-Messung, Kapazitäts-Spannungs-Messung, Thermische Admittanz- Spektroskopie (TAS) und Deep Level Transient Spectroscopy (DLTS) verwendet. Ergänzend wurden die auf weitbandlückige Halbleiter ausgelegten Verfahren Low Rate Deep Level Transient Spectroscopy (LR-DLTS) und Deep Level Optical Spectroscopy (DLOS) eingesetzt, mit welchen es möglich ist Defektzustände in der gesamten Bandlücke von ZnO nachzuweisen. Für die untersuchten Störstellenniveaus konnten somit die thermische Aktivierungsenergie, Einfangquerschnitte freier Ladungsträger und Photoionisationsquerschnitte bestimmt werden.
Typischerweise werden tiefe Defekte durch die Bestrahlung mit hochenergetischen Protonen erzeugt. Derartige Behandlungen wurden an binären ZnO- und ternären (Mg,Zn)ODünnfilmen durchgeführt, wobei die Generationsrate eines Defektes über Variation der verwendeten Strahlungsdosis bestimmt wurde. Ionenimplantationen spielen eine große Rolle im Herstellungsprozess von Bauelementen, sind jedoch für ZnO nicht etabliert. Die Auswirkung der Implantation von inerten Argon-Ionen, sowie die nachträgliche thermische Behandlung auf die Konzentration intrinsischer Defekte wurde untersucht. Zink- und Sauerstoff-Implantationen bewirken, neben der Generation von Defekten, eine lokale Änderung der Stöchiometrie. Durch einen Vergleich der Defektkonzentrationen nach Zn-, O-, Ne- und Ar-Implantation können Rückschlüsse auf die chemische Natur intrinsischer Defekte geschlossen werden.:1 Einleitung
I Grundlagen
2 Elektronische Eigenschaften von Defekten in Halbleitern
2.1 Typen und Klassifizierung von Defekten
2.2 Lokalisierte Zustände in Halbleitern
2.2.1 Donatoren und Akzeptoren
2.2.2 Flache Defekte und effektive Masse-Näherung
2.2.3 Tiefe Defekte
2.3 Besetzungsstatistik und Ratengleichungen
2.3.1 Thermische Emission
2.3.2 Optische Emission
2.3.3 Nichtstrahlender Einfang und Multiphononen Emission
2.3.4 Arrhenius Auswertung
2.3.5 Zeitentwicklung des Besetzungsgrades
3 Raumladungszonenspektroskopie
3.1 Metall-Halbleiter-Kontakte
3.2 Kapazitätstransienten
3.3 Kapazitäts-Spannungs-Messungen (C(U))
3.4 Thermische Admittanz Spektroskopie (TAS)
3.5 Deep level transient spectroscopy (DLTS)
3.6 Konzentrationsbestimmung
3.7 Laplace-Deep level transient spectroscopy (LDLTS)
3.7.1 Entstehung des LDLTS-Signals
3.7.2 Einschränkungen der Methode
3.8 Deep level optical spectroscopy (DLOS)
4 Die Halbleiter ZnO und MgZnO
4.1 Kristallstruktur und Gitterparameter
4.2 Bandstruktur
4.3 ZnO als transparentes leitendes Oxid
4.4 Defekte in ZnO
5 Probenherstellung und Charakterisierung
5.1 ZnO-Züchtung
5.1.1 ZnO-Volumenkristalle
5.1.2 ZnO-Dünnfilme
5.2 Kathodenzerstäubung
5.3 Protonenbestrahlung und Ionenimplantation
5.3.1 Bremsquerschnitt
5.3.2 Protonenbestrahlung
5.3.3 Ionenimplantation
5.4 Probenaufbau und Schottky-Kontakte
5.5 Raumladungszonenspektroskopie-Messplatz
5.6 Rasterkraftmikroskopie
5.7 Kelvinsondenkraftmikroskopie
5.8 Röntgendiffraktometrie
5.9 Photolumineszenzspektroskopie
II Charakterisierung züchtungsinduzierter Defekte
6 Defekte in ZnO-Volumenkristallen und -Dünnfilmen
6.1 Elektrische Eigenschaften
6.2 Thermische Admittanz-Spektroskopie
6.3 Deep-level transient spectroscopy
6.4 E3 und E3’ in ZnO Dünnfilmen
6.4.1 Low Rate – DLTS
6.4.2 Laplace-DLTS
6.4.3 thermisch aktivierter Einfang von E3’
6.5 Einfluss thermischer Nachbehandlung
6.6 Einfluss der Züchtungstemperatur
6.7 Die Meyer-Neldel Regel
6.8 E7, TH1 und T4 in ZnO – DLOS
6.8.1 Raumtemperatur DLOS des ZnO-Volumenkristall
6.8.2 Raumtemperatur DLOS des ZnO-Dünnfilm
6.8.3 DLOS-Messungen bei tiefen Temperaturen
6.9 Optische Anregung von E3’ in ZnO-Dünnfilmen
7 Defekte in (Mg,Zn)O-Dünnfilmen
7.1 (Mg,Zn)O-Dünnfilme auf a-Saphir
7.2 Photolumineszenz
7.3 XRD
7.4 DLTS-Untersuchungen
7.5 E3 in verspannten (Mg,Zn)O-Filmen
7.6 DLOS – T4 und TH1 in (Mg,Zn)O-Dünnfilmen
7.7 Zusammenfassung
8 Einfluss der Wachtumsorientierung auf die Defektstruktur von ZnO-Dünnfilmen
8.1 ZnO-Dünnfilme auf a-, m- und r-Saphir
8.2 Strukturelle Eigenschaften
8.3 Photolumineszenz
8.4 Elektrische Eigenschaften
8.5 Defektsignaturen
III Charakterisierung strahlungsinduzierter Defekte
9 Protonenbestrahlung an (Mg,Zn)O-Dünnfilmen
9.1 Der E4-Defekt in ZnO – Stand der Literatur
9.2 E4 in polaren (Mg,Zn)O-Dünnfilmen
9.2.1 Probenaufbau und Protonenbestrahlung
9.2.2 Elektrische Eigenschaften
9.2.3 DLTS-Untersuchungen
9.3 E4 in unpolaren ZnO-Dünnfilmen
9.4 Zusammenfassung
10 Defekte in Argon-implantierten ZnO-Dünnfilmen
10.1 Probenstruktur und Ionenimplantation
10.2 Thermische DLTS
10.3 DLTS mit monochromatischer Anregung
11 Defekte in Zn- und O-implantierten ZnO-Dünnfilmen
11.1 Proben und Ionenimplantation
11.2 Nettodotierkonzentration
11.3 Thermische DLTS
11.4 DLOS
11.5 Defekte mit geringen Konzentrationen – E470 und E390
12 Zusammenfassung und Ausblick