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1
Mirjalili, Ghazanfar. "Far infrared characterisation of GaN epilayers." Thesis, University of Essex, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339240.
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Wang, Yingjuan. "Comprehensive optical spectroscopic investigations of GaN epilayers and InGaN/GaN quantum structures." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37090343.
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Wang, Hongjiang, and 王泓江. "Spectroscopic investigation of optical properties of GaN epilayers andInGaN/GaN quantum wells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B29779911.
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Wang, Yingjuan, and 王穎娟. "Comprehensive optical spectroscopic investigations of GaN epilayers and InGaN/GaN quantum structures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37090343.
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Junaid, Muhammad. "Magnetron Sputter Epitaxy of GaN Epilayers and Nanorods." Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-84655.
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In this research, electronic-grade GaN(0001) epilayers and nanorods have been grown onto Al2O3(0001) and Si(111) substrates, respectively, by reactive magnetron sputter epitaxy (MSE) using liquid Ga as a sputtering target. MSE, employing ultra high vacuum conditions, high-purity source materials, and lowenergy ion assisted deposition from substrate biasing, is a scalable method, lending itself to large area GaN synthesis. For the growth of epitaxial GaN films two types of sputtering techniques, direct current (DC) magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) were studied. The GaN epitaxial films grown by DC-MSE directly on to Al2O3(0001) in a mixture of Ar and N2, feature low threading dislocation densities on the order of ≤ 1010 cm-2, as determined by transmission electron microscopy (TEM) and modified Williamson-Hall plots. X-ray rocking curves reveal a narrow full-width at half maximum (FWHM) of 1054 arcsec of the 0002 reflection. A sharp 4 K photoluminescence (PL) peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. GaN(0001) epitaxial films grown on Al2O3 substrates by HiPIMS deposition in a mixed N2/Ar discharge contain both strained domains and almost relaxed domains in the same epilayers, which was determined by a combination of x-ray diffraction (XRD), TEM, atomic force microscopy (AFM), μ-Raman microscopy, μ-PL, and Cathodoluminescence (CL). The almost fully relaxed domains show superior structural and optical properties evidenced by a rocking curves with full width at half maximum of 885 arc sec and a low temperature band edge luminescence at 3.47 eV with the FWHM of 10 meV. The other domain exhibits a 14 times higher isotropic strain component, which is due to higher densities of point and extended defects, resulting from bombardment of energetic species during growth. Single-crystal GaN(0001) nanorods have been grown directly on Si(111) substrates by DC-MSE in a pure N2environment. The as-grown GaN nanorods exhibit very high crystal quality from bottom to the top without any stacking faults, as determined by TEM. The crystal quality is found to increase with increasing working pressure. XRD results show that all the rods are highly 0001 oriented. All nanorods exhibit an N-polarity, as determined by convergent beam electron diffraction methods. Sharp and well-resolved 4 K μ-PL peaks at ~3.474 eV with a FWHM ranging from 1.7 meV to 22 meV are attributed to the intrinsic GaN band edge emission and corroborate the exceptional crystal quality of the material. Texture measurements reveal that the rods have random in-plane orientation when grown on Si(111) with its native oxide while they have an inplane epitaxial relationship of GaN[11̅20] // Si[1̅10] when grown on Si(111) without the surface oxide. The best structural and optical properties of the rods were achieved at N2 partial pressures of 15 to 20 mTorr. By diluting the reactive N2 working gas in DC-MSE with Ar, it is possible to achieve favorable growth conditions for high quality GaN nanorods onto Si(111) at a low total pressure of 5 mTorr. With an addition of small amount of Ar (0.5 mTorr), we observe an increase in nanorod aspect ratio from 8 to ~35, a decrease in average diameter from 74 nm to 35 nm, and a 2-fold increase in nanorod density compared to pure N2 conditions. By further dilution, the aspect ratio continuously decreases to 14 while the diameter increases to 60 nm and the nanorod density increases to a maximum of 2.4×109 cm-1. The changes in nanorod morphology upon Ar-dilution of the N2 working gas are explained by a transition from N-rich growth conditions, promoting the diffusion induced nanorods growth mode, to Ga-rich growth conditions, in qualitative agreement with GaN nanorods growth by MBE. At N2 partial pressure of 2.5 mTorr, the Ga-target is close to a non-poisoned state which gives the most perfect crystal quality which is reflected in an exceptionally narrow band edge emission at 3.479 eV with a FWHM of only 1.7 meV. Such structural and optical properties are comparable to rods previously grown at 3 to 4 time higher total working pressures of pure N2.
6
Zhang, Fan, and 張帆. "Photoluminescence and reflectance spectra of Si-doped GaN epilayers." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43278565.
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Zhang, Fan. "Photoluminescence and reflectance spectra of Si-doped GaN epilayers." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43278565.
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Bulbul, Mahir Mehmet. "Raman spectroscopy of GaN epilayers and InGaAlAs quaternary semiconductor alloys." Thesis, University of Essex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242232.
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Hao, Rui. "Structural and optical characterisations of defects in non-polar and semi-polar GaN epilayers and InGaN/GaN MQWs." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610548.
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Kendrick, Chito Edsel. "Revisiting Nitride Semiconductors: Epilayers, p-Type Doping and Nanowires." Thesis, University of Canterbury. Electrical and Computer Engineering, 2008. http://hdl.handle.net/10092/2108.
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This dissertation investigates the growth of high quality GaN and InN thin films by plasma assisted molecular beam epitaxy (PAMBE). It also explores the growth of self-seeded GaN branching nanowires and p-type doping of InN, two topics of particular interest at present.
The growth of high quality III-Nitride semiconductor thin films have been shown to be dependent on the group-III (metal) to nitrogen ratio. A metal-rich growth environment enhances the diffusion of the group-III adatoms through the formation of a group-III adlayer. By using a metal-rich growth environment, determined by growth rate studies using laser reflection interferometry or RHEED analysis of the surface, both GaN and InN films have been grown with a smooth surface morphology. Additionally the smooth surface morphology has beneficial effects on the electrical and optical properties of both materials. However, with the growth using a metal-rich environment, group-III droplets are present on all film surfaces, which can be an issue for device fabrication, as they produce facets in the crystal structure due to enhanced growth rates.
MBE growth of GaN nanowires via the vapour liquid solid (VLS) and vapour solid (VS) growth techniques have so far been based on the N-rich growth regime. However, we have shown that the Ga-rich growth regime can be used to grow self-seeded one dimensional and hierarchical GaN nanowires. 7 µm long hierarchical GaN nanowires with at least three branches were grown and shown to have a high crystalline quality. The suggested growth mechanism is a self-seeding VLS process driven by liquid phase epitaxy at the nanoscale, while the branching growth was nucleated due to the Ga-rich growth regime by excess Ga droplets forming on the trunk during growth. The growth of vertical GaN nanowires has also been achieved using the same self-seeding process and the critical parameter seems to be the Ga to N ratio. Also, the growth rate of the Ga-rich grown GaN nanowires can supersede the growth rates reported from N-rich grown GaN nanowires by at least a factor of two.
The fabrication of vertical and planar GaN nanowire devices has been demonstrated in this study. Two point and three point contacts were fabricated to the branching GaN nanowires in the planar direction with resistive measurements ranging from 200 - 900 kΩ, similar to chemical vapour deposition and MBE grown GaN nanowires. The nonlinear current-voltage characteristics from the three point contacts may lead to unique nano-devices. The planar nanowires have also shown to have potential as UV detectors. Schottky diodes were fabricated on the vertical nanowires, with values for the barrier heights consistent with bulk diodes.
Mg and Zn doping studies of InN were also performed. Both InN:Mg and InN:Zn have strong photoluminescence only at low doping concentrations. However, the InN:Mg films have reduced mobilities with increased Mg content, whereas the mobility determined from the InN:Zn films is independent of Zn. When the InN:Zn film quality was improved by growing under the In-rich growth regime, electrochemical capacitance-voltage results suggest n{type conductivity, and strong photoluminescence was obtained from all of the films with four features seen at 0.719 eV, 0.668 eV, 0.602 eV and 0.547 eV. The features at 0.719 eV and 0.668 eV are possibly due to a near band edge to valence band or shallow acceptor transition, while the 0.547 eV has an activation energy of 60 meV suggesting a deep level acceptor.
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Vemuru, Ajay Sandeep. "Experimental and Theoretical Investigation of Absorption and Emission Cross-Sections in Rare Earth Doped GaN Epilayers." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1219459189.
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Pierce, Jonathan Mark. "Growth and Characterization of Epitaxial ZnO Thin Films on GaN(0001) Epilayers and ZnO{0001} Substrates Using Metalorganic Chemical Vapor Depositon." NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-06282004-090927/.
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ZnO thin films were produced on GaN(0001) epilayers and ZnO(0001) substrates utilizing an iterative process requiring a structured low temperature (480°C) layer followed by a high temperature (800°C) densification step to create approximately 200 nm of contiguous film. This process is subsequently repeated to achieve thicker films with each iteration producing approximately 200 nm of dense film. Diethylzinc was used as the zinc source, UHP oxygen (O2) as the oxygen source, and UHP argon as both the carrier and diluent gas. Nitrous (N2O) and nitric oxide (NO2) were also used both as potential oxygen sources in the pure state as well as mixed with oxygen in the chamber and for nitrogen doping of the growing film. Major impurities of C, H, and N were incorporated into the films with the majority of the incorporation occurring during the low temperature step. Films grown using N2O + O2 contained an average of 5 x 1017 cm-3 atomic nitrogen while films using NO2 + O2 had an average nitrogen concentrations of 9 x 1019 cm-3. Needle microstructures were observed for low temperature layers using O2 and N2O + O2, while networked structures formed when using NO2 + O2. The surface of the densified films contained hexagonal pits that increased in number and depth with an increase in film thickness. Triple-axis XRD measurements indicated that the crystal structure of the films mimic the underlying substrates. A comparative analysis of undoped and N-doped films using capacitance voltage and photoluminescence measurements showed that the N-doped films were more insulating than the undoped films and the incorporation of nitrogen decreases the amount of excitonic peaks observed in the PL spectra. The 3.367 eV ionized donor bound exciton becomes dominant in N-doped films relative to the 3.361 eV donor bound exciton that dominates the undoped films. A preliminary inductively coupled plasma etching study determined that the smoothest sidewalls and surfaces were obtained using an ICP power of 600 W, a DC bias of 50 V, 5 mtorr total pressure, and 20 sccm of pure flowing BCl3 The etch rate under these conditions was 40 nm/min.
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Obradovic, Bojan. "Light scattering and luminescence of InGanN epilayers." Thesis, University of Essex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343546.
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Wang, Jielei Ms. "Optical Properties of In1-xGaxN Epilayers Grown by HPCVD." Digital Archive @ GSU, 2010. http://digitalarchive.gsu.edu/phy_astr_theses/9.
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Optical absorption spectroscopy has been applied to study properties such as the fundamental absorption edge and defect absorption centers of group III-nitride compound semiconductor epilayers. The investigation in this thesis focused on analyzing the band gap of indium-rich In1-xGaxN epilayers, which where grown by the high-pressure chemical vapor deposition (HPCVD) technique. Our results - together with literature data for gallium-rich In1-xGaxN alloys indicate that the shift of the fundamental band gap of In1-xGaxN with composition x can be described with a bowing parameter of b = 2.2eV. Temperature dependent transmission measurements show that the band gap variation with temperature follows a S-shape behavior for small gallium concentration and shifts towards a Varshni type behavior for a higher gallium concentrations. The S-shape behavior is attributed to nanoscale compositional fluctuations/clustering in the ternary alloy system. The thicknesses of the measured In1-xGaxN epilayers have been analyzed through multilayer stack model calculations of the transmission spectra. The free electron concentration in the In1-xGaxN epilayers has been obtained from simulations of infrared reflectance spectra.
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Hussein, Emad Hameed. "Fabrication and characterization of GaP/Si nanodiode array based on nanowires synthesized from GaP epilayers grown on Si substrates." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17693.
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In dieser Arbeit wird das epitaktische Wachstum von GaP/Si Heterostrukturen zur Herstellung von rauscharmen GaP/Si Nanodiodenarrays untersucht, wobei eine top-down Ätztechnik zur Herstellung der verwendeten Nanodiodenarrays genutzt wurde. Zur Untersuchung der gewachsenen Schichten wurden Röntgenstreuung (XRD), Rasterelektronenmikroskopie sowie die elektrische Charakterisierung mittels Strom-Spannungs und Kapazität-Spannungsmessungen verwendet. Zudem wurde die Grenzfläche zwischen epitaktischer Schicht und Substrat mittels Niederfrequenter Rauschspektroskopie (LFN) untersucht. Die GaP-Schichten wurden auf p-dotierten Si (100) Substraten mittels eines Riber-32P Gasquellen-Molekularstrahlepitaxiesystems gewachsen. Die Abhängigkeit der Oberflächenbeschaffenheit und Kristallqualität von denWachstumsbedingungen, wie der Wachstumstemperatur, wurden intensiv untersucht, um die Defektdichte zu minimieren. Dafür wurden nominal 500 nm dicke Heterostrukturschichten beiWachstumstemperaturen von 550 °C, 400 °C und 250 °C gewachsen, wobei 400 °C als die optimale Wachstumstemperatur bestimmt wurde. Trotzdem waren die erhaltenen Schichten aufgrund der hohen Versetzungsdichte von schlechter Qualität. Eine nur sehr geringe Qualitätsverbesserung konnte durch einen in situ durchgeführten thermischen Annealingschritt bei 500 °C für 10 Minuten erreicht werden. Daher wurde eine neue Annealingmethode vorgeschlagen, die in dieser Arbeit step-graded annealing (SGA) genannt wird. Bei dieser Methode wurde die Temperatur schrittweise von 400 °C auf 480 °C innerhalb von 90 Minuten erhöht. Dabei wurde die Oberfläche die gesamte Zeit mittels Reflexion hochenergetischer Elektronen (RHEED) untersucht. Die Oberflächenrekonstruktion, die während des Annealens mittels RHEED beobachtet wurde, zeigte schließlich eine große Verbesserung der Kristallqualität. Die Gitterparameter von GaP wurden mittels asymmetrischer XRD gemessen, wobei festgestellt wurde, dass sie exakt denen von Volumen-GaP entsprechen. Zudem wurde festgestellt, dass die GaP-Schicht automatisch n-dotiert ist und diodentypisches Gleichrichtungsverhalten aufweist. Interessante Informationen über Fallenzustände in den Heterostrukturfilmen konnten mittels LFN-Messungen gefunden werden. In einer nicht annealten Probe wurden beispielsweise zwei Fallenzustände im Bereich der Bandlücke festgestellt. In den mittels der SGA-Methode annealten Proben wurde hingegen ein rauscharmes und fallenfreies System erhalten. Anschließend wurde Elektronenstrahllithografie (EBL) zum Erstellen von Nanomustern auf der Oberfläche genutzt, die zur Herstellung von Nanodrähten genutzt werden sollen. Zur Optimierung der Elektronenstrahllithografie wurden dabei GaPSubstrate aufgrund der im Vergleich zu den epitaktischen Schichten besseren und glatteren Oberflächenstruktur genutzt. Dabei konnten in einer Goldschicht 200 nm große Löcher in einem Gitter mit hoher Dichte auf GaP erstellt und in die GaPSchicht übertragen werden. Die metallunterstütztes chemisches Ätzen (MacEtch) genannte Technik wurde kürzlich vorgeschlagen und eignet sich für die Herstellung von Nanodrähten. Die Anwendung zur Herstellung von Nanodrähten aus GaP war herausfordernd aufgrund bisher begrenzter Anwendung für III-V Halbleiter. Zur Optimierung der MacEtch Technik wurde zunächst wieder GaP-Substrat verwendet, um den Einfluss von Kristalldefekten und der Oberflächenrauigkeit auf die Ergebnisse zu minimieren. Genutzt wurde ein Gemisch aus Lösungen von HF/KMnO4 mit verschiedenen Konzentrationen. Mit den so bestimmten Prozessbedingungen konnten erfolgreich GaP Nanodrähte aus GaP-Epilayern hergestellt werden. GaP/Si Heteroübergangsnanodioden wurden anschließend unter Nutzung von Au-Ge/Ni Kontakten zu GaP-Schicht und Al/Ni Kontakten zum rückseitigen Si hergestellt. Die Transporteigenschaften des Nanodiodenarrays bestätigen die Möglichkeit, diese Arrays als elektronische NiederLärmbauelemente einzusetzen.An epitaxial growth of GaP/Si heterostructures for the fabrication of low-noise GaP/Si nanodiode array based on nanowires is reported. The grown films were characterized using X-ray diffraction, scanning-electron microscopy, atomic-force microscopy and electrical measurements. Besides that, the interface between the epilayer and the substrate was deeply studied using a low-frequency noise (LFN) spectroscopy. The GaP epilayers were grown on p-type Si (100)substrates using gas-source molecular-beam epitaxy system. The dependence of surface morphology and crystal quality on the growth conditions was intensively investigated for minimizing the defects. The heterostructure films were grown at an optimal growth temperature of 400 °C and a nominal thickness of 500 nm. In order to improve the crystalline quality of the heterostructures, a new thermal annealing method was proposed, and referred to as step-graded annealing (SGA). In this method, the temperature was increased gradually to the annealing temperature to reduce the strain relaxation in the epilayers. A highly improvement in the crystal quality was confirmed using the SGA method. In addition, the epilayers were found to be n-type autodoped, and exhibited diode rectification behavior. Furthermore, the trap levels in the band gap, which were revealed via LFN measurements, were found to be suppressed in the annealed films. Thereafter, gold-mesh nanopatterns on the GaP surfaces were fabricated using an electron-beam lithography, as a step for the fabrication of GaP nanowires. A metal-assisted chemical etching technique with a mixture of HF:KMnO4 was carried out to fabricate GaP nanowires. GaP/Si heterojunction nanodiodes were then fabricated using an Au-Ge/Ni contact on the top of the GaP nanowires as well as an Al/Ni contact on the backside of Si. Transport properties of the nanodiode array confirmed the possibility of using the array as a low-frequency electronic device.
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Chao, Wei-Chou, and 趙偉州. "Study on GaN Epilayers Prepared by OMCVD." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/55020775830953010642.
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碩士國立中山大學
電機工程研究所
85
The materials based on GaN have been successfully developed on short-wavelength laser diodes (LDs) and light-emitting diodes (LEDs). In this study, GaN epilayers have been successfully grown on sapphire substrates. We used several methods including the growth of the GaN buffer layer, nitridation process before the growth and the adjustment of the vertical distance between the outlet of group-Ⅲ to the substrate on graphite to the growth of GaN epilayers. From the results of the photoluminescence (PL) measured at 77K and the X-Ray diffraction measurement, we get the better qualities of the GaN epilayers after using the foregoing methods. In this study, the optimal results of the 77K PL measurement and X-Ray diffraction measurement were 51 meV and 191 arcsec.
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Pan, Yung-Chung, and 潘永中. "Growth and Characterizations of InN and GaN Epilayers." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/74533607794198918716.
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博士國立交通大學
電子物理系
89
We have carried out systematic studies on epitaxial growth of both InN and GaN compounds using metalorganic vapor phase epitaxy technique (MOVPE). Regarding InN, experimental data indicated that its crystalline properties depend strongly on TMIn flow rate and the growth temperature. The deposited hexagonal InN film seems to comprise two major components: one is mosaic crystallites and the other is fiber-like structures. Raman data reflect that the hexagonal structure is predominant for InN film prepared at high growth temperatures, whereas cubic/hexagonal mixing prevailing at temperatures below 450℃. Besides, pregrowth treatments such as nitridation temperature and nitridation duration also have profound effects on InN film quality. By optimizing the growth parameters, we can obtain InN films with X-ray linewidth, Raman E2 mode bandwidth, Hall mobility, and carrier concentration of 96 arcsec, 4.5 cm-1, 270 cm2/V.s, and 5×1019 cm-3, respectively. These values, to our knowledge, are among the best ones ever reported for such type of film. As far as GaN is concerned, we have found that the film quality is very sensitive to the procedures adapted in low-temperature nucleation layer growth, including growth temperature and thickness. Besides, growth rate, nitridation conduction, V/III ratio as well as mixed carrier gas also have great influences on GaN deposition. The optimum growth parameters in our study are as follows: nucleation layer thickness＝375A (520℃), ramping rate＝100℃/min, growth temperature＝1,075℃, growth rate＝0.8 mm/hr, 1,050℃ nitridation temperature = 2 min, V/III ratio＝3,000, and pure N2 carrier gas of flow rate = 2,000 sccm. As a consequence, GaN film with good Hall properties of 300 cm2/V.s and 1×1017 cm-3 can be realized by our reactor, which conceivably is a prerequisite for further p-type GaN growth study. For GaN:Mg growth, results indicate that the Mg atoms can easily incorporate into GaN film and saturate at a value of about 1020 cm-3. When saturation occurs, blue shift of A1(LO) Raman mode presents, concurrently with the appearance of TO modes, which strongly suggesting a mixing of cubic phase in the hexagonal structure. This assertion is also confirmed by Ga K-edge and N K-edge X-ray absorption measurements. Extended X-ray absorption region of the spectra (EXAFS) from Ga K-edge further reveals the induced defects comprising primarily vacancies, substitutions, and interstitial occupations. They are formed anisotropically in the crystal either along c-axis direction or on its perpendicular plane and lead to disorderliness of the doped GaN films. This feature is believed to be one of the essential factors responsible for the high compensation, hence poor Hall properties of Mg-doped p-type GaN film. Nevertheless, extraordinary high hole concentration ( ~3×1018 cm-3) and low resistivity (~0.2 W-cm) are obtained for a GaN:Mg sample annealed at 700℃ for 45 min. The corresponding 10% activation efficiency, which is well above a typical value of ~1%, to our best knowledge is among the best records ever reported for such type of film.
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Yang, Min-Hao, and 楊閔皓. "Fabrication of thin-film LEDs using GaN-on-Si epilayers." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/fpu39z.
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碩士國立中興大學
材料科學與工程學系所
101
In this thesis, thin-film blue light-emitting diodes (LEDs) using GaN-on-Si(111) epilayers were fabricated via wafer bonding and substrate removal processes. As compared to the common sapphire substrate, the Si substrate has better properties in electrical conductivity, thermal conductivity, and thermal stability. The substrate-free LEDs were expected to show a higher efficiency and better heat dissipation due to the improvement of current crowding issue. Moreover, the Ag/In bonding layer was also used to enhance the thermal dissipation, and hence reduce the degree of droop in LED efficiency. To understand the influence on LED performances, three kinds of LEDs were prepared in this study. They are named as the lateral LEDs (L-LEDs), secondary-transferred LEDs (S-LEDs), and vertical-structured LEDs (V-LEDs). At an injection current of 700 mA, the light output power of L-LEDs, S-LEDs and V-LEDs were 90.88, 155.87 and 261.07 mW, respectively. Obviously, the light output power of S-LEDs and V-LEDs were enhanced by 71.5 and 187.3 % compared to that of L-LEDs. The surface temperatures of L-LEDs, S-LEDs and V-LEDs were measured to be 90.72, 76.7, and 58.1 °C, respectively. The results clearly indicate that the good performance of LED devices can be achieved by using a thin-film device configuration.
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Mita, Seiji. "Polarity control in GaN epilayers grown by metalorganic chemical vapor deposition." 2007. http://www.lib.ncsu.edu/theses/available/etd-07192007-114246/unrestricted/etd.pdf.
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Tai, Wen-Chieh, and 戴文傑. "Growth and characterization of low-dislocation GaN epilayers using SiN interlayer." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/62290883003989933708.
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碩士國立交通大學
電子物理系所
102
In this thesis, we use Metalorganic Chemical Vapor Deposition (MOCVD) reactor to growth GaN epilayer. We insert SiN layer before main eplayer, and by varying SiH4 flow rate, we can control SiN coverage condition and the growth mode of GaN on top of it. We then perform Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Photoluminescence (PL) experiments. From SEM result, we know that the SiN coverage condition will affect GaN island density on top of SiN, which led to uncoalescence surface when flow rate as high as 80nmol/min. We calculate dislocation density from XRD result, and a-type dislocation density decrease with increasing SiH4 flow rate until the film can’t coalescence (From 8×108 cm-2 to 2×108 cm-2), then it increase again. The reason is dislocation bending during 3D growth, it increase the probability of dislocation reaction and annihilation, but when the film fail to coalescence, this mechanism is hindered, so the dislocation density rise again. In the end, the PL result shows up to 4x intensity increase by reducing dislocation density from 8×108 cm-2 to 2×108 cm-2.
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Song, T. L., Soo-Jin Chua, Eugene A. Fitzgerald, Peng Chen, and S. Tripathy. "Plastic Relaxation In Single InᵡGa₁âᵡN/GaN Epilayers Grown On Sapphire." 2003. http://hdl.handle.net/1721.1/3839.
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Plastic relaxation was observed in InᵡGa₁âᵡN/GaN epilayers grown on c-plane sapphire substrates. The relaxation obeys the universal hyperbolic relation between the strain and the reciprocal of the layer thickness. Plastic relaxation in this material system reveals that there is no discontinuous relaxation at critical thickness and once a layer starts to relieve, it follows the same strain-thickness dependence, unconstrained by the original misfit until the material system work hardens. From x-ray diffraction calibration, the in-plane and normal relaxation constants KP0 and KN0 for the InᵡGa₁âᵡN/GaN grown on sapphire were found to be â0.98 ± 0.03 and +0.51 ± 0.03 nm, respectively.Singapore-MIT Alliance (SMA)
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Chua, Soo-Jin, Eugene A. Fitzgerald, and T. L. Song. "Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epilayers Grown on sapphire." 2003. http://hdl.handle.net/1721.1/3723.
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Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain and to annihilate the dislocations that build up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled and thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10 nm GaN grown at 750 0°C and annealed at 1000 0°C.Singapore-MIT Alliance (SMA)
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Lin, Yu-Sheng, and 林佑昇. "Characterizations of GaN epilayers on nanoscale patterned c-plane sapphire substrates for LEDs." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/87083841548921967812.
Full textAbstract:
博士國立清華大學
奈米工程與微系統研究所
100
Recently, GaN-based wide bandgap semiconductors are very important material system for fabrication of light emitting devices (LEDs) in a wide range of wavelength. The GaN-based laser diodes (LDs) and LEDs have been widely used in many areas, such as optical storage, backlight in liquid crystal displays, traffic signal and solid state lighting. High external quantum efficiency (EQE) of LEDs with high crystalline quality are urgently demanded for achieving high performance LEDs on nanoscale patterned c-plane sapphire substrates (c-NPSS) technologies. This work is carried out not only to realize high performance c-plane GaN-based LEDs but also to project the high quality of nonpolar GaN epitaxy on c-NPSS. This dissertation explores the fabrication, structural properties, and physical features, optical and electronic properties of polar and nonpolar GaN epilayers grown on c-NPSS. The main focus of this dissertation can be divided into four parts. First part is the fabrication of c-NPSS by inductively coupled plasma-reactive ion etching (ICP-RIE) with different materials as nano-masks for enhancing the light extraction and improving crystalline quality. Second part is the optical characterization of c-NPSS with different feature sizes. The formation of the c-NPSS is employed by ICP-RIE with self-assemble nickel silicides as the nano-masks. The optimal feature size was presented with high transmittance over broadband spectra. The transmittance of visible to near-IR spectra was found to be 95% at normal incidence and over 90% at an incident angle of 45 degree. In the mid-IR spectrum, the transmittance exceeds 88% until the reflection is no longer suppressed by nanostructures. The polarization properties have also been investigated. The nanostructures can enhance the reflectivity ratio 90% for wavelengths shorter than 400 nm. As the amplitude ratio, enhanced from 50% to 80% over the whole visible spectrum. Next part is the morphology of c-NPSS has two designs, one is c-facet sapphire dominated (c-NPSS-c) and the other is n-facet sapphire dominated (c-NPSS-n). The formation of the nanostructures is employed by ICP-RIE with polysilicon as the nano-masks formed by low pressure chemical vapor deposition and wet-etching methods. The polar and nonpolar GaN epilayers was grown on c-NPSS using MOCVD. This part focus on the fabrication and optical properties are investigated using AFM for surface morphology, high resolution XRD for crystalline orientation, TRPL for crystalline quality, and SEM and TEM for growth/structure analysis. The GaN epilayers were characterized by XRD and AFM, which reveals the GaN epilayer can be c-plane (0001) or m-plane (10-10) orientation depending on the surface morphology of nanopatterned sapphire substrate. The corresponding full width at half maximum (FWHM) of the X-ray rocking curves (XRC) for c- and m-plane GaN are 211 and 316 arcsec, respectively. The root-mean-square (rms) surface roughness was measured to be 0.30 nm by AFM. The pits density on GaN surface improved two orders of magnitude than that on convenitional sapphire substrate (CSS) by AFM. The last part presents the comparison of GaN-based LEDs grown on c-NPSS-c and CSS. The fabrication, electronic properties and light output performance of GaN-based LEDs are analyzed in detail. The optical and structural properties are investigated by using XRD, electroluminescence (EL) measurement, SEM, and high resolution TEM. The LEDs fabricated on c-NPSS-c exhibit an output power of 33.10 mW at a driving current of 20 mA, which is 2.38-fold higher than that on CSS. In addition, the corresponding EQE are 58.30% and 24.50% for LED on c-NPSS-c and CSS, respectively.
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陳永翔. "Growth and Characterizations of Low Temperature GaN Epilayers Using Two-Heater MOCVD Reactor." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/94735309950732283879.
Full textAbstract:
碩士國立交通大學
電子物理系所
100
In this theses, we use the home-made two-heater MOCVD reactor to grow low-growth temperature(850 ℃) GaN (LT-GaN) thin films. The electrical and optical properties of these samples were investigated by Hall, X-ray diffraction and photoluminescence measurements. Hall measurement results indicate that the optimized V/III ratio of LT-GaN thin films grown by two-heater MOCVD reactor is 10000. The carrier concentration and carrier mobility of LT-GaN thin films is 3.9x1018 cm-3 and 146 cm2/Vs. The LT-photoluminescence (19 K) result shows that the emission is dominated by near band emission. The X-ray diffraction and temperature dependent Hall measurement (TD-Hall measurement) are employed to confirm the scattering mechanism. The X-ray diffraction spectra show that the dislocation density does not change significantly with the various V/III ratios, implying that the dislocations scattering is insignificant in V/III series of GaN films. The TD-Hall measurements indicate that the native defects scattering is the dominated scattering mechanism.
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WU, SHU-WEI, and 吳書緯. "Optical properties of ZnO epilayers and InGaN/GaN mulitiple-quantum-well light emitting diodes." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/25041550914615132975.
Full textAbstract:
碩士中原大學
應用物理研究所
96
We studied the optical properties of the InGaN/GaN mulitiple-quantum-well light emitting diodes (LEDs) and ZnO epilayers. Using photoconductivity and photoluminescence, the carrier escape efficiency and nonradiative efficiency of the InGaN/GaN multiple-quantum-well LEDs can be obtained. The electroluminescence (EL) intensity of the InGaN/GaN mulitiple-quantum-well LEDs is increased by about 1.1-2.1 times after incorporation of the gold nanoclusters. It is found the experimental enhancement of luminescence is in good agreement with the simulated result from the Mie scattering. We therefore suggest the scattering of the gold nanoclusters is responsible for the enhancement of EL. We also studied the energy relaxation of hot electrons in ZnO epilayers using PL. The measured electron temperature variation with different electric fields can be explained by two different models based on the energy relaxation of electrons due to LO phonon and acoustical phonon scattering. We find the energy relaxation of the hot electrons in ZnO epilayers is dominated by the acoustics phonon scattering at low temperature. As the temperature increases, the LO phonon scattering plays an important role in the energy relaxation of the hot electrons gradually.
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Chang, Yu-Wei, and 張祐維. "Characterization of AlxGa1-xN Epilayers and AlGaN/GaN 2DEG Heterostructures Grown by Molecular Beam Epitaxy." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/79gfsv.
Full textAbstract:
碩士國立交通大學
電子物理系所
106
A high crystal quality GaN channel layer, a series of 0% to 100% AlxGa1-xN ternary alloy, and AlGaN/GaN two-dimensional electron gas (2DEG) heterostructures have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) on MOCVD-grown semi-insulating GaN templates. A wide range of measurements were conducted on the GaN channel layer samples, AlxGa1-xN samples, and 2DEG samples to study the interplay between their characteristics. A high sheet carrier concentration of 1.42×1013 cm-2 and a low sheet resistance of 599 Ω / sq were achieved by performing different treatments at the AlGaN/GaN heterointerface. However, the mobility of the 2DEG was rather low and the values were scattered from sample to sample, presumably due to the unoptimized GaN surface morphology and Al content fluctuation in the AlGaN barrier layer.
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Hsiao, Yuan-Chun, and 蕭元駿. "The Study of multi-Nanoindentation and Cathodoluminescence measurement on A-axis GaN epilayers mechanical characteristics." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/31208268589511217643.
Full textAbstract:
碩士國立交通大學
機械工程學系
98
The purpose of this study is to investigate the effect of nanomechanical properties and relative cathodoluminescence characteristics on A-plane gallium nitride (GaN) epilayers. In the experiment procedure, the high quality GaN epilayers was synthesized by metal-organic chemical vapor deposition (MOCVD) on prismatic A-planes (1120) of sapphire substrate. Two different loading modes were utilized to observe plastic deformation behavior and the nanomechanical properties of GaN epilayers in nanoindentation process. After that, the surface morphologies and failure mechanism of indentation-induced deformed area were analyzed by using Atomic Force Microscopy (AFM) and cathodoluminescence system, respectively. The varied elastoplastic deformation behaviors were obtained by using different loading modes which cause different lattice sliding and dislocation nucleation mechanisms in GaN epilayers. Besides, the degradation of peak intensity and shift of peak wavelength were observed from cathodoluminescence analyses. These variations were due to the generation of large dislocations and changed lattice constant through loading process.
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Wang, Bo-Yan, and 王博彥. "Studies of (I) the influence of Mn composition on CdMnTe epilayers grown on Si substrate and (II) the effect of silicon doping in part of barriers on 8 periods InGaN/GaN quantum wells." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/j493pm.
Full textAbstract:
碩士國立臺南大學
材料科學系碩士班
103
There are two parts in this research. The first part is the study of effects of Mn content in Cd1-xMnxTe grown by molecular beam epitaxy (MBE) on silicon (Si) (111) substrate. Owing to different binding energy of atoms, Te-Te binding shows the lower forming energy than Cd-Te, results in the production of Te-Te binding defects. Incorporation of Mn atoms into CdTe demonstrates that the lower binding energy of Mn-Te than Te-Te can cause the reduction of Te-Te binding defects in CdTe:Mn. In this report, the ternary alloy of Cd1-xMnxTe with Mn content in 0, 2, 21 % were prepared. The integrated intensity of photoluminescence (PL) spectra exhibits three times larger than other samples in sample with Mn content 21 %. The Stokes shift (SS) characterized by peak energy of PL spectra and bandgap energy of photoreflectance (PR) spectra show the greater value in Mn 21 % than others. The results indicate that the larger the Mn content in Cd1-xMnxTe, the more the composition fluctuations of Mn content in Cd1-xMnxTe showing larger SS. Scan electron microscope (SEM) images give the direct behavior of materialmicrostructures. The results indicates that Mn 21 % sample have relatively flat surface of the film. Micro-Raman spectra also exhibit the diminished intensity of scattering modes of A1 and E that are related to Te-Te binding defects. The consequence is that the better condition of Mn content is 21 % in Cd1-xMnxTe for superior optical and material properties. The second part of the research is the study of optical behaviors of blue light emitting diodes (LEDs) with multiple quantum wells (MQs) containing part of Si doping. The Si doping layers are the first two, three, four, and five barriers of QWs in the growth sequence from sapphire substrate of four samples. The results indicate that the reduction of piezoelectric field in QWs were occurred in all samples for the blue shift in PL peak energy compared with the undoped Si sample. First four Si-doped barrier samples show larger PL spectra intensity with greater carrier localization in QWs and smaller quantum confined Stark effect (QCSE). Soft confinement potential of QWs was observed in first four Si-doped barrier samples due to the existence of strong absorption intensity in the bandgap energy between quantum wells and barriers. The uniform spreading of carriers in QWs were expected in this sample. Blue LED with first four Si-doped barrier, thus having better output power and external quantum efficiency (EQE) under high current injection. Therefore, first four Si-doped barrier is the favorite condition for light emission of blue LED having 8 QWs.
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Mahesh, Kumar *. "Group III-Nitride Epi And Nanostructures On Si(111) By Molecular Beam Epitaxy." Thesis, 2011. http://hdl.handle.net/2005/2408.
Full textAbstract:
The present work has been focused on the growth of Group III-nitride epitaxial layers and nanostructures on Si (111) substrates by plasma-assisted molecular beam epitaxy. Silicon is regarded as a promising substrate for III-nitrides, since it is available in large quantity, at low cost and compatible to microelectronics device processing. However, three-dimensional island growth is unavoidable for the direct growth of GaN on Si (111) because of the extreme lattice and thermal expansion coefficient mismatch. To overcome these difficulties, by introducing β-Si3N4 buffer layer, the yellow luminescence free GaN can be grow on Si (111) substrate. The overall research work carried out in the present study comprises of five main parts. In the first part, high quality, crack free and smooth surface of GaN and InN epilayers were grown on Si(111) substrate using the substrate nitridation process. Crystalline quality and surface roughness of the GaN and InN layers are extremely sensitive to nitridation conditions such as nitridation temperature and time. Raman and PL studies indicate that the GaN film obtained by the nitridation sequences has less tensile stress and optically good. The optical band gaps of InN are obtained between ~0.73 to 0.78 eV and the blueshift of absorption edge can be induced by background electron concentration. The higher electron concentration brings in the larger blueshift, due to a possible Burstein–Moss effect. InN epilayers were also grown on GaN/Si(111) substrate by varying the growth parameters such as indium flux, substrate temperature and RF power.
In the second part, InGaN/Si, GaN/Si3N4/n-Si and InN/Si3N4/n-Si heterostructures were fabricated and temperature dependent electrical transport behaviors were studied. Current density-voltage plots (J-V-T) of InGaN/Si heterostructure revealed that the ideality factor and Schottky barrier height are temperature dependent and the incorrect values of the Richardson’s constant produced, suggests an inhomogeneous barrier at the heterostructure interface. The higher value of the ideality factor compared to the ideal value and its temperature dependence suggest that the current transport is primarily dominated by thermionic field emission rather than thermionic emission. The valence band offset of GaN/β-Si3N4/Si and InGaN/Si heterojunctions were determined by X-ray photoemission spectroscopy. InN QDs on Si(111) substrate by droplet epitaxy and S-K growth method were grown in the third part. Single-crystalline structure of InN QDs (droplet epitaxy) was verified by TEM and the chemical bonding configurations of InN QDs were examined by XPS. The interdigitated electrode pattern was created and (I-V) characteristics of InN QDs were studied in a metal–semiconductor–metal configuration in the temperature range of 80–300 K. The I-V characteristics of lateral grown InN QDs were explained by using the trap model. A systematic manipulation of the morphology, optical emission and structural properties of InN/Si (111) QDs (S-K method) is demonstrated by changing the growth kinetics parameters such as flux rate and growth time. The growth kinetics of the QDs has been studied through the scaling method and observed that the distribution of dot sizes, for samples grown under varying conditions, has followed the scaling function.
In the fourth part, InN nanorods (NRs) were grown on Si(111) and current transport properties of NRs/Si heterojunctions were studied. The rapid rise and decay of infrared on/off characteristics of InN NRs/Si heterojunction indicate that the device is highly sensitive to the IR light. Self-aligned GaN nanodots were grown on semi-insulating Si(111) substrate. The interdigitated electrode pattern was created on nanodots using photolithography and dark as well as UV photocurrent were studied. Surface band gaps of InN QDs were estimated from scanning tunneling spectroscopy (STS) I-V curves in the last part. It is found that band gap is strongly dependent on the size of InN QDs. The observed size-dependent STS band gap energy blueshifts as the QD’s diameter or height was reduced.
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Li, Yen-Chi, and 李彥其. "Temperature-dependent Hall measurement on undoped GaN epilayer." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/98405530657372519600.
Full textAbstract:
碩士國立中山大學
物理學系研究所
92
The temperature-dependent Hall measurement was performed on the undoped GaN thin films grown by molecular beam epitaxy. The mobility and electron density were obtained by the T-dependent ( 4.2K~300K ) Hall measurement at magnetic field 300mT. Since the Hall coefficient is the ratio of the perpendicular electric field to the product of current density and magnetic field, we calculate the mobility and electron density to get the temperature-dependent mobility and electron density curves. We change the N/Ga ratio on the epilayer of two samples and analysis the mobility and carrier density against temperature. The sample growth procedure were (1)nitridation for 60 min, with ,at .(2) low temperature GaN buffer layer growth for 2 min, with ,at , and (3)high temperature GaN epilayer growth for 3hr, at . The N/Ga ratio of the samples are 30 and 35.
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Rajpalke, Mohana K. "Semipolar And Nonpolar Group III-Nitride Heterostructures By Plasma-Assisted Molecular Beam Epitaxy." Thesis, 2012. http://hdl.handle.net/2005/2483.
Full textAbstract:
Group III-nitride semiconductors are well suited for the fabrication of devices including visible-ultraviolet light emitting diodes, high-temperature and high-frequency devices. The wurtzite III-nitride based heterostructures grown along polar c-direction have large internal electric fields due to discontinuities in spontaneous and piezoelectric polarizations. For optoelectronic devices, such as light-emitting diodes and laser diodes, the internal electric field is deleterious as it causes a spatial separation of electron and hole wave functions in the quantum wells, which decreases emission efficiency. Growth of GaN-based heterostructures in alternative orientations, which have reduced (semipolar) or no polarization (nonpolar) in the growth direction, has been a major area of research in the last few years. The correlation between structural, optical and transport properties of semipolar and nonpolar III-nitride would be extremely useful. The thesis focuses on the growth and characterizations of semipolar and nonpolar III-nitride heterostructures by plasma-assisted molecular beam epitaxy.
Chapter 1 provides a brief introduction to the III-nitride semiconductors. The importance of semipolar and nonpolar III-nitride heterostructures over conventional polar heterostructures has been discussed.
Chapter 2 deals with the descriptions of molecular beam epitaxy system and working principles of different characterization tools used in the present work.
Chapter 3 addresses the molecular beam epitaxial growth of nonpolar (1 1 -2 0) and semipolar (1 1 -2 2) GaN on sapphire substrates. An in-plane orientation relationship is found to be [0 0 0 1] GaN || [-1 1 0 1] sapphire and [-1 1 0 0] GaN || [1 1 -2 0] sapphire for nonpolar GaN on r-sapphire substrates. Effect of growth temperature on structural, morphological and optical properties of nonpolar GaN has been studied. The growth temperature plays a major role in controlling crystal quality, morphology and emission properties of nonpolar a-plane GaN. The a-plane GaN shows crystalline anisotropy nature and it has reduced with increase in the growth temperature. The surface roughness was found to decrease with increase in growth temperature and film grown at 760°C shows reasonably smooth surface with roughness 3.05 nm. Room temperature photoluminescence spectra show near band emission peak at 3.434 -3.442 eV. The film grown at 800 ºC shows broad yellow luminescence peak at
2.2 eV. Low temperature photoluminescence spectra show near band emission at 3.483 eV along with defect related emissions. Raman spectra exhibit blue shift due to compressive strain in the film. An in-plane orientation relationship is found to be [1 -1 00] GaN || [1 2-1 0] sapphire and [-1 -1 2 3] GaN || [0 0 0 1] sapphire for semipolar GaN on m-plane sapphire substrates. The surface morphology of semipolar GaN film is found to be reasonably smooth with pits on the surface. Room temperature photoluminescence shows the near band emission (NBE) at 3.432 eV, which is slightly blue shifted compared to the bulk GaN. The Raman E2 (high) peak position observed at 569.1 cm1.
Chapter 4 deals with the fabrication and characterizations of Au/nonpolar and Au/semipolar GaN schottky diodes. The temperature-dependent current–voltage measurements have been used to determine the current mechanisms in Schottky diodes fabricated on nonpolar a-plane GaN and semipolar GaN epilayers. The barrier height (φb) and ideally factor (η) estimated from the thermionic emission model are found to be temperature dependent in nature indicate the deviations from the thermionic emission (TE) transport mechanism. Low temperature I-V characteristics of Au/ GaN Schottky diode show temperature independent tunnelling parameter. Barrier heights calculated from XPS are found to be 0.96 eV and 1.13 eV for Au/nonpolar GaN and Au/semipolar GaN respectively.
Chapter 5 demonstrates the growth of InN on r-sapphire substrates with and without GaN buffer layer. InN film and nanostructures are grown on r-sapphire without GaN buffer layer and they are highly oriented along (0002) direction. The electron microscopy study confirms the nanostructures are vertically aligned and highly oriented along the (0001) direction. The Raman studies of InN nanostructures show the SO modes along with the other possible Raman modes. The band gap of InN nanostructures is found to be 0.82 eV. InN grown with a-plane GaN buffer shows nonpolar orientated growth. Growth temperature dependent studies of nonpolar a-plane InN epilayers are carried out. The valence band offset value is calculated to be 1.31 eV for nonpolar a-plane InN/GaN heterojunctions. The heterojunctions form in the type-I straddling configuration with a conduction band offsets of 1.41 eV.
Chapter 6 deals with the temperature dependent I-V characteristics of the nonpolar a-plane (1 1 -2 0) InN/GaN heterostructures. The measured values of barrier height and ideality factor from the TE model show the temperature dependent variation. The double Gaussian distribution has mean barrier height values ( ϕb ) of 1.17 and 0.69 eV with standard deviation (σs ) of 0.17 and 0.098 V, respectively. The modified Richardson plot ln (Is/T2)-q2σ2/2k2T2 ) versus q/kT in the temperature range of 350 – 500 K, yielded the Richardson constant of 19.5 A/cm2 K2 which is very close to the theoretical value of 24 A/cm2 K2 for n-type GaN. The tunneling parameters E0 found to be temperature independent at low temperature range (150 –300 K).
Chapter 7 concludes with the summary of present investigations and the scope for future work.
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Tu, Jen-Hung, and &;#20931;任鴻. "Defect Characterization of GaN Epilayer Template for LED Applications." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/84358428630812387930.
Full textAbstract:
碩士國立中興大學
材料科學與工程學系所
98
In this thesis, we report an approach for efficiently improving the threading dislocation (TD) density and internal quantum efficiency of InGaN-based near-ultraviolet (~400 nm) light-emitting diodes (LEDs). A combination of selective etching of GaN defects and patterned sapphire substrate (PSS) techniques forms a growth mask of TDs in GaN epitaxial layers. This selective etched-GaN/PSS structure can efficiently achieve defect centralization and the defect density can be reduced to 105 cm-2. The structural properties of the regrown GaN epilayers were investigated in details using double-crystal X-ray diffraction, cathodeluminescence, and secondary ion mass spectroscopy. Under a 350-mA injection current, the output power of the SiO2-block/PSS LED is enhanced by 46% compared with that of the conventional GaN/sapphire one. The improvement of the output power is not only due to the decrease in dislocation density, but also to the enhancement of extraction efficiency using PSS. In addition, we investigate the characteristics of near-ultraviolet (~400 nm) InGaN multiple-quantum well based LED using a SiLENS simulation program. Simulations of light-output power versus current are performed for GaInN/GaN light-emitting diodes grown on GaN-on-sapphire templates with different threading dislocation densities. The energy band diagrams, carrier concentrations, radiative recombination efficiency, light-current curves, and external quantum efficiency are taken into account in detail. Low-defect-density devices exhibit a efficiency peak followed by droop as current increases. However, the high-defect-density devices show low peak efficiencies and little droop. The simulation results suggest that improvement of internal quantum efficiency is mainly due to the increase of radiative recombination at high current injection.
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Lee, Yuan-Jyun, and 李元鈞. "Optimization of GaN and AlN epilayer for HEMT application." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/m3an56.
Full textAbstract:
碩士國立交通大學
電子物理系所
106
GaN, Al1-xGaxN, and AlN epilayers were grown by molecular beam epitaxy system (MBE). The in situ reflection high-energy electron diffraction (RHEED) measurements were used to find the best growth conditions of substrate temperature and element flux ratio. The optical properties and surface morphology were analyzed by photoluminescence (PL), cathodoluminescence (CL), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, the electrical properties of two dimensional electron gas (2DEG) of AlN/GaN heterostructure were investigated by the Hall measurements. By the control of substrate temperature and Ga/N ratio, the luminescence signal from Ga vacancy could be suppressed and a better surface roughness about 0.4 nm for GaN was achieved. In the case of Al1-xGaxN growth, the substrate temperature was fixed at 740 oC for high Al composition samples. By using the migration enhanced epitaxy (MEE) for the interface expitaxy of AlN/GaN heterostructure, the decomposition of GaN channel layer can be significantly suppressed. The raising substrate temperature to 740 oC enhances migration of the AlN to fill the surface pits. It improves the electron mobility up to 988 (cm2/V•s) in 2DEG.
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Lin, PeiYen, and 林沛彥. "The Growth Mechanism of GaN V-defect and Novel Method for GaN Epilayer Transfer." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/55113576717688067712.
Full textAbstract:
碩士國立交通大學
材料科學與工程系
90
This thesis investigates and discusses the formation mechanism of V-defect on GaN epilayer based on the appearance of large V-defect. Although facets and crystal shape of large V-defect and dot patternd GaN ELOG are similar, they are not the same from the thermodynamic and kinetic point of view based on calculated total free energy. V-defect is a result of an unstable energy of state so the appearance of V-defect is mostly likely resulted from the kinetic control during epitaxy process. The discussion of the formation of V-defect is divided into two parts: nucleation and growth. Nucleation step is related to the change of polarity of certain area on GaN epitaxy film; growth step is influenced by the different growth rate of different facets. Change in polarity on epitaxy film is due to the defect that is generated during the deposition of epitaxy film. The polarity of a certain area changes the growth rate of that specific area and thus nucleates a V-defect. After nucleation, V-defect turns into growth up or elimination depend on comparing of (0001) and facets of GaN which affected by different growth conditions. By previous research, the facets growth rate may change by varying temperature, pressure, V/III ratio, and dopant. We suppose upper factors are associate with Ga diffuse and bonding abilities. Better Ga diffuse ability and lower bonding probability may cause facet growth faster. The “nucleation and grwoth” model can reasonable explain both previous experience evidences without any exception and the formation of large V-defect. This thesis also introduces a novel GaN epilayer transfer method. This method combines ELOG GaN, wafer bonding technology, and selective wet etching to acheieve the purpose of integration a high quality GaN film on a selective substrate. By preliminary evaluation, the novel method has many advantages and worth to advanced research.
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Wang, Jen-Yu, and 王振宇. "Investigation of Different Buffer Layer Conditions on GaN Epilayer Characteristics." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/33093444982945114821.
Full textAbstract:
碩士國立彰化師範大學
光電科技研究所
96
It has been well known that the high mismatch in lattice constant andthemal expansion coefficients between Si and GaN causes cracks andhigh density of dislocations when GaN is grown on Si substrate. Thesedefects deteriorate GaN film characteristics. In this thesis, the effect ofdifferent buffer-layers on GaN epilayer characteristics was investigated. In chapter one, properties of GaN-based compound materials are firstintroduced. In chapter two, the operation principles of several instruments used for experiments as well as GaN crystal growth related papers were reviewed. In chapter three, the effects of AlN buffer thickness, III/V ratio of AlN nucleation layer, GaN/AlN superlattice structure and low-growth-rate GaN buffer layer on GaN epilayer characteristics were investigated. Experimental result indicates that GaN crystalline quality is enhanced using thinner AlN buffer thickness owing to dislocation density between GaN/AlN interface is reduced. The XRD -scan at GaN(0002) peak and the RT-PL FWHM are 0.35o and 78 meV, respectively. Moreover, AlN/GaN superlattice and low growth rate GaN buffer layer can also be used to reduce the dislocation densities. However, the epitaxial growth condition still needs to be optimized.
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Hsieh, Chi-Ying, and 謝奇穎. "Study of GaN epilayer quality improvement using defect selective passivation technique." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/21503166390545428269.
Full textAbstract:
碩士國立交通大學
影像與生醫光電研究所
100
In recent decades, the III-nitrides become an interesting class of wide band-gap materials and play an important role in semiconductor devices. GaN-based light emitting devices have attracted great attention in last decade due to its importance in solid state lighting applications. The GaN-based device are full color LED displays, white LEDs and high capacity storage devices. However, GaN-LEDs still require further improvement of optical output power. To successfully fabricate high efficient LED depends on the high quality GaN epilayer with low defect density. In previous work, we demonstrated that the defect selective passivation method could reduce defect density and enhance LED performance. In this thesis, we simplify the process of defect selective passivation technique by spin-coating silica nanospheres on GaN surface to block the propagation of dislocations. Moreover, we apply defect selective passivation technique to fabricate high efficient LED. The analysis of photoluminescence, cathodoluminecence and electroluminescence show the crystal quality of GaN epilayer is improved.
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Wang, Hao-Yu, and 王浩宇. "Growth of ZnO Nanorod Epilayer on GaN/Sapphire by aqueous solution deposition." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/06905107357615650681.
Full textAbstract:
碩士中原大學
電子工程研究所
105
Transparent and high electron mobility thin film transistor (TFT) is the key technology for modern displays. The transparency can enhance the brightness of display at lower operated power. The high electron mobility can enhance the switching speed and resolution. Metal oxides, for example zinc oxide (ZnO) can meet those requirements. In this study, we grow ZnO nanorod array and transform into ZnO epilayer on p-type GaN/sapphire substrate by aqueous solution deposition (ASD). The XRD analysis shows the good crystalline quality of ASD-ZnO epilayer after N2O annealing. The PL analysis of ZnO epilayer shows the typical emissions of near band edge excitonic emission (NBE) peak at 376 nm and deep level emission (DLE) (550~650 nm) bands. The deep level emission (550~650 nm) is composite to O vacancies and Zn interstitial, the emission is improved after N2O annealing at 300 °C. In addition, AFM shows ASD-ZnO can obtain a smooth and continuous epilayer. The morphology and thickness of ZnO epilayer we obtained by the analyses of FE-SEM and the electrical properties of ZnO epilayer were characterized by Hall measurement. In order to increase the growth rate of epilayer and enhance the merge of ZnO nanorods, HNO3 solution incorporation is promising for the growth of ZnO epilayer transformed from ZnO nanorod array. ASD-ZnO epilayer with and without HNO3 incorporation is compared in this study.
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Chen, Ching-Wei, and 陳晉瑋. "X-ray characterization of GaN epilayer and InxGa1-xN multiple quantum wells." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/76538950559332899273.
Full textAbstract:
碩士國立清華大學
工程與系統科學系
89
In this work we use X-ray diffraction to analyze the microstructures of two III-nitride sample systems. The first part of sample systems is cubic-GaN epilayers MBE-grown on GaAs(001) of assorted Ga flux ratio from 0.8, 1.0, 1.1, to 1.2; the second part is the InxGa1-xN-GaN multiple quantum wells on sapphire, varied with the fractional molar value of In- composition: x = 0.1~0.25, nominally. Starting from the focus of polytype GaN as revealed by conventional X-ray diffraction, we derive a correlation of the light-emitting efficiency with different Ga flux ratio to the crystalline quality of microstructures. It is simply confirmed that the Ga-poor sample of Ga flux ratio 0.8 shows worse quality both on the emission peak of 380-nm photoluminescence and on the diffraction width of zinc-blende crystalline structures. While, after a rigorous examination on the purposed cubic-GaN films from Ga-poor to Ga-rich, we do not resolve any difference in the lattice constants. On the other side, the lattice constant c of the wurtzite phases mixed in the GaN film gradually expands as the Ga flux ratio getting increased. We conjecture that, in Ga-rich samples, extra Ga atoms would occupy the interstitial sites in wurtzite domains to play a role as impurity-like defects. Consequently, as if the wurtzite domains had a better crystalline quality, the overall thin film would suffer more stress and yield a worse efficiency in the light emission. In view of the orientation spheres, the geometric correlation and domain distributions of the primary and twined wurtzite phases are properly reconstructed with respect to the cubic-GaN lattice. We conclude that the origin of wurtzite domains is due to the stacking fault and twin bands prevailing in the GaN film. Following after the study of GaN epilayers, but taking advantage of bright and well-collimated synchrotron X-rays, we apply high-resolution X-ray diffraction to characterize the superlattice structure of InxGa1-xN multiple quantum wells. Preliminary results have been done to precisely determine the thickness of periodic InxGa1-xN-GaN bilayers and to assure the indium composition as compared with the nominal value x. All of our analyses are straightly based upon a linear regression from the peak positions of superlattice reflections, which is less dependent of the details presumed in a strain-layer model.
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劉建呈. "Investigation of In-rich InGaN Epilayer Grown on GaN Template Using Varied Buffer Structures." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/98503408359891196473.
Full textAbstract:
碩士國立彰化師範大學
光電科技研究所
98
In this thesis, growth conditions and characteristics of c-axis oriented In-rich InGaN epilayers grown on GaN template using molecular beam epitaxy (MBE) were studied. In chapter one, fundamental characteristics and applications of In-rich InGaN materials were first introduced. In chapter two, some literatures related to In-rich InGaN epi-growth were reviewed. In these literatures, different buffers and substrates were utilized to grow In-rich InGaN epi-films. The qualities of In-rich InGaN epilayers grown on either GaN or InN templates can be greatly improved and better than the ones grown directly on sapphire substrate. However, there was no firmed conclusion on which buffer was better. Therefore, in this thesis, various buffer layers were utilized and inserted between In-rich InGaN epi-layers and GaN templates to investigate the characteristics of In-rich InGaN epilayers. In chapter three, various buffer layer structures including low-growth-rate GaN buffer, low temperature InGaN buffer and InN buffer layers for In-rich InGaN epilayer grown on GaN templates were first described. The Ⅴ/Ⅲ ratio of stoichiometry condition for growing In-rich InGaN epi-layer was then determined and the growth temperature was chosen to be 525 °C. From experimental results, the full-widths at half maximum (FWHM) of X-ray diffraction rocking curve (XRDRC) for (002) and (102) In-rich InGaN were 0.072° and 0.62° by inserting a 3-nm low temperature InGaN buffer between low-growth-rate GaN buffer layer (LGR-GaN) and InGaN epilayers. The surface morphology of InGaN epi-layer was further improved with a higher growth temperature of 550 °C. Finally, the XRDRC FWHM for (102) InGaN can be reduced to 0.58° if the growth temperature of LGR-GaN buffer was decreased to 750°C. Finally, conclusion and future work of thesis are given in chapter 4.
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Hsieh, ChengYu, and 謝承佑. "Improvement of Epitaxy GaN Quality Using Nano-Patterned Sapphire Substrates and Grown Semipolar GaN Epilayer on a-Plane Patterned Sapphire Substrates." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/61348192573753092307.
Full textAbstract:
博士國立交通大學
材料科學與工程學系
101
High brightness emissing diodes (LEDs) have been highly demand in various fields like using on road light, car headlight, backlight and projector. For the purpose of next-generation application of solid-state lighting, LEDs with higher internal and external quantum efficiency are required. Among many methods, lots of efforts have been invested on patterned sapphire substrates (PSS) to improve the quality of GaN film and light extraction efficiency. In first part of this study, a relatively simple, easy and inexpensive liquid-phase deposition (LPD) method was used to fabricate PSS. Besides, if GaN is grown on c-plane sapphire, a built-in polar will decrease the recombination efficiency in active layers and also cause red-shift in wave length. In second part of this study, a-plane PSS is fabricated and expect to reduce this effect. In the first part, a simple, easy and relatively inexpensive liquid phase deposition (LPD) method was used to introduce nano SiO2 on sapphire substrates to fabricate nanoscale patterned sapphire substrates (PSS). Three kinds of nanoscale PSS were used to grow GaN, namely “NPOS” which is nano-pattern oxide on sapphire substrate and “NPSS” which is nano-patterned sapphire substrate and “MNPSS” which is modified nano-patterned sapphire substrate. It was found that upper region of MNPSS-GaN had the best quality. This is because as the growth time increased, laterally-grown GaN caused the threading dislocations to bend toward the patterns. Besides, voids formed on the MNPSS pattern sidewalls caused more threading dislocation bending toward these voids. In the second part, a (1 0 1-4) semipolar GaN layer was grown on periodic stripe patterned a-plane sapphire substrate fabricated by using two-steps etching process. The stripes in prism shape were inclined with sapphire c-axis in 60 degrees. The orientation relationship between semipolar GaN and sapphire is (0 0 0 2)GaN // (2 1-1-3)sapphire and [21-10]GaN // [235-2]sapphire as defined by selected area diffraction in transmission electron microscopy (TEM). Growth of semipolar GaN on the sidewalls of the prism stripes is evidenced from TEM and x-ray φ scan. The quality of semipolar GaN film is reasonably good as examined with x-ray rocking curves. In addition, TEM and cathodoluminescence results show that the dislocation density in the semipolar GaN is significantly reduced near the film surface.
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Shen, Meng-wei, and 沈孟緯. "Structure and morphology of GaN epilayer grown by multi-step method with molecular-beam epitaxy." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/uq76kp.
Full textAbstract:
碩士國立中山大學
物理學系研究所
95
Abstract In this literary, we discuss with structure and morphology improvement of GaN epilayer on c-sapphire by multi-step method in molecular-beam epitaxy. Our research is caused for the critical results of defect in GaN epilayer and rough surface morphology. In order to solve these problems we used a novel technique which we called multi-step method. In this thesis, the results of X-ray, SEM, AFM all demonstrated the achievement in our composition. However, we obtained the results of full width of half maxima (FWHM) of (0002) and (10 2) XRD rocking curves with 60~120 arcseconds and 700~ 1200 arcseconds from a series of multi-step samples respectively. Comparing with previous measurement, multi-step method is relatively superior, and the measurement of AFM roughness is under 2 nm from the series of multi-step samples. If we discuss the flat area further, we can get smoother surface which roughness is about 0.4 nm. It is obviously to recognize the flat and rough regions, but in SEM image we made sure that the flat region occupied the greater part of surface. So, in this literary we verified that the method of multi-step can improve the structure and morphology of GaN by molecular-beam epitaxy.
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Guan, Zhen-Zhong, and 官振中. "Study of GaN epilayer on Si(111) substrates with superlattices and low-growth-rate buffer layers." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/50078829200414300846.
Full textAbstract:
碩士國立彰化師範大學
光電科技研究所
97
In this thesis, the characteristics of GaN epilayers grown on Si(111) substrates were studied using two different buffer layers. One is to insert GaN/AlN superlattices before growing GaN epilayer. The other is to grown low-growth-rate (LGR) GaN buffer before growing GaN epilayer. This thesis has been divided into five chapters. In chapter one, properties of GaN-based compound materials were introduced. In chapter two, some literatures of GaN epilayer growth were reviewed. In chapter three, molecular beam epitaxy (MBE) system and experimental procedures were introduced. In chapter four, the effects of GaN/AlN superlattices and LGR GaN buffer layers on GaN epilayer characteristics were investigated and discussed. The analysis facilities include: scanning electron microscopy (SEM), X-Ray diffraction (XRD), atomic force microscope (AFM), photoluminescence (PL), and transmission electron microscopy (TEM). Regarding GaN/AlN superlattice buffers, different growth conditions have been studied including growth temperature, superlattice thickness, superlattice period and buffer layer structures grown before GaN/AlN superlattices. The growth temperature of superlattices was determined to be 750 ℃. The experiemtnal results also indicated GaN epilayers with thinner superlatices and more superlattice periods had better XRD full width at half maximum (FWHM). However, when the superlattices were too thin, nucleation in superlattices seemed incomplete which caused rough surface morphology. Moreover, inserting an AlGaN epi-layer with low Al composition or a GaN layer before growing GaN/AlN superlattice did not obtain better results. Optimization in growth parameters should be further investigated. Regarding LGR-GaN buffers, the effect of LGR-GaN thickness has been studied. When the growth time of LGR-GaN was 3 minutes, the XRD FWHMs was 0.29, which was the best value. Experimental results indicated that a thick LGR GaN was not beneficial to the surface morphology and XRD FWHM owing to the rough morphology of LGR GaN growth. Further study could be done by raising LGR-GaN growth temperature or changing LGR GaN growth rate.
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卓昕如. "Fabrication of nano-sized patterned sapphire substrate by Liquid Phase Deposition for the Growth of GaN epilayer." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/01581398021350588544.
Full textAbstract:
碩士國立交通大學
材料科學與工程學系
99
Fabrication of pattern sapphire substrate(PSS) through a standard photolithography process, which includes mask forming and etching steps, is the major approach to manufacture conventional PSS. However, the resolution limit of photolithography makes nano-sized PSS(NPSS) hard to realize. In this study, chemical liquid-phase deposition(LPD) method is applied to NPSS fabrication and the effect on crystal quality of GaN epitaxial layer brought by NPSS has been discussed. By LPD and wet etching process, NPSS has been successfully fabricated. Compared to GaN grown on planar c-sapphire, the GaN epilayer grown on NPSS has better crystal quality, which is confirmed by the XRD and EPD data. Between NPSS-60 and NPSS-90, the former shows better crystal quality because of its lower c-plane ratio and proper distance between patterns. Modified NPSS, which is fabricated by keeping top LPD-SiO2 on NPSS, can bring further improvement of crystal quality, and the XRD and SEM data shows that the oxide on pattern has no obvious destruction of crystal quality. In ch4, GaN epitaxy directly proceeds on sapphire substrate with LPD-SiO2 pattern. GaN grown on such substrate has better crystal quality. Dislocation bending is observed through TEM analysis, which means the improvement of crystal quality is mainly from increase of lateral growth region.
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Chiang, Lieh-Kuan, and 江烈寬. "Effect of thickness of epilayer of GaN on nature of band bending by contactless electroreflectance and photoreflectance." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/2j2s84.
Full textAbstract:
碩士國立中山大學
物理學系研究所
95
The wurtzite GaN has either Ga or N polarity. The direction of polarization, hence it’s associated polarization-induced electric fields (Fp), is determined by the polarity of the sample. In the present work, we prepared both N-face polarity and n-type doping of GaN with thicknesses are 1.1μm and 70nm. Photoreflectacne (PR) and contactless electroreflectance (CER) were used in combination to study the nature of the surface band bending which was found to be determined by the type of doping for the thick sample and by the polarity for the polarity for the thin sample. This is in agreement with a theoretical calculation by Poisson-Schrödinger solver. Hence, CER can determine the polarity of GaN film as long as the sample is thin enough of the Fp to become dominant in the surface region.
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Lee, Chia-En, and 李佳恩. "Study of Light Extraction Enhancement for GaN-based Light Emitting Diodes by Flip-Chip and Epilayer-Transfer Technology." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/68407178879630131201.
Full textAbstract:
博士國立交通大學
光電工程系所
98
In the thesis, we report the flip-chip and epilayer-transferred types GaN-based LEDs for improving the light extraction efficiency of devices. In the part of flip-chip type LEDs, the light-emitting diodes (FC-LEDs) with micro-pillar-array structure, the FC-LEDs with geometric oblique sapphire structure, and FC-LEDs with triple light scattering layers were investigated. In the first part, the micro pillar arrays structure is formed on the bottom side of sapphire substrate by dry etching process to increase the light-extraction efficiency. The light output power of the FC-LED is increased by 68% for a 3.2 μm textured micro pillar on the bottom side of the sapphire substrate. Our work offers promising potential for enhancing output powers of commercial light-emitting devices. In the second part, the sapphire shaping structure is formed on the bottom side of sapphire substrate by chemical wet etching technique for light extraction purpose. The crystallography-etched facets are (1-106), (11-25) and (1-102) plane against the (0001) c-axis with the angles range between ~30°- ~60°. These large slope oblique sidewalls and greatly thick sapphire windows layer are useful for enhancing light extraction efficiency. The light output power of sapphire shaping FC-LEDs (SSFC-LEDs) was increased 55 % (@ 350 mA current injection) compared to that of conventional FC-LEDs (CFC-LEDs). In the third part, the FC-LEDs with triple light scattering layers were demonstrated by conjunction with the epi-growth on micro-pillar array sapphire substrate and naturally textured p-GaN surface. The totally internal reflection effect could be effectively reduced between the GaN-air, GaN-sapphire, and sapphire-air interfaces. The light output of the FC-LEDs with triple light scattering layer structure was increased about 60% (@350 mA current injection). The epilayer-transferred type LEDs were fabricated by the combination of wafer bonding and laser lift-off techniques to transfer the GaN epilayer to a better thermal dissipation and conductive substrate. In this part, the epilayer-transferred type LEDs with modified surface structures were demonstrated including roughened mesh surface and photonic crystal surface structures. In the first part, the epilayer-transferred type LEDs with the roughened mesh surface were proposed by transferring the GaN epilayer which was grown on a pattern sapphire substrate to a high thermal conductivity and electrical conductive silicon substrate and roughening the mesh surface by chemical wet etching process. Under 350 mA current injection, the epilayer-transferred type LEDs with the roughened mesh surface presents a further enhancement of 20% in output power comparing with that of regular epilayer-transferred type LEDs. In the second part, the epilayer-transferred types LEDs with the 8-folds photonic crystal surface structure were demonstrated. By adopting a photonic crystal surface structure, the light extraction efficiency was effectively improved. In addition, a Lambertian far-field pattern was also realized.