Дисертації з теми "InxGa1-xN"

Os semicondutores baseados no InxGa1-xN são amplamente utilizados em dispositivos emissores de luz num conjunto diverso de novas aplicações tecnológicas. O conhecimento das propriedades físicas deste material tem progredido a um ritmo mais lento do que a tecnologia. No entanto, para que se concebam dispositivos no domínio da optoelectrónica adequados a necessidades específicas, é essencial adquirir um conhecimento profundo sobre a física fundamental deste sistema. O presente trabalho de dissertação teve como objectivo fundamental o estudo das propriedades vibracionais da liga semicondutora de InxGa1-xN, com recurso à técnica de dispersão de Raman. Os filmes de InxGa1-xN que se caracterizaram foram crescidos epitaxialmente, por Deposição Química em Fase de Vapor, utilizando um substrato de GaN/safira. Combinando as diferentes técnicas de caracterização, óptica (espectroscopia Raman, Fotoluminescência e Absorção) e estrutural (Microscopia Electrónica de Varrimento, Espectrometria de Dispersão de Rutherford e Difracção de Raios X), foi possível separar, com sucesso, os efeitos da tensão e da composição na frequência do fonão A1(LO) do InxGa1-xN. Consequentemente, foram determinados os respectivos potenciais de deformação e estabeleceu-se a dependência da frequência do fonão A1(LO) em função da composição da liga. O processo de relaxação da rede do InxGa1-xN, ao longo da direcção de crescimento, foi investigado, num conjunto de amostras sujeitas a um desbaste químico controlado, com recurso à espectroscopia Raman. Este estudo permitiu consolidar toda a interpretação dos resultados experimentais relativos à frequência e à forma espectral do fonão A1(LO). Paralelamente ao estudo da dinâmica de rede, e em resultado deste ter implicado a identificação das energias de absorção e de emissão associadas a transições electrónicas, foi identificada e caracterizada a emissão a 1.88 eV observada numa amostra de do InxGa1-xN parcialmente relaxada. Finalmente foi realizado um estudo, com vista a avaliar a receptividade da matriz de InxGa1-xN à introdução, por implantação iónica, de iões de terrasraras, em particular o Er3+. Em consequência foi investigada a luminescência a ~1.5 μm, associada à transição intraiónica do estado excitado (4I13/2 ) para o estado fundamental (4I15/2). Os resultados mostraram que a incorporação de iões na rede de InxGa1-xN por implantação iónica não é o método mais adequado.
Semiconductors based on InxGa1-xN are widely used in light emitting devices, in a novel array of technological applications. The knowledge of the fundamental physical properties of this material has been progressing at a slower rate than the fast paced technological development. However, in order to develop devices tailored to specific needs, a deep knowledge of the physics of this system is mandatory. The main purpose of the research work was the study of the vibrational properties of the semiconductor alloy of InxGa1-xN, through the use of Raman dispersion technique. The InxGa1-xN films that were characterized were epitaxially grown by chemical vapour deposition, over a GaN/sapphire subtract. Through the combined use of different characterization techniques, optical (Raman spectroscopy, Photoluminescence and Absorption) and structural (Scanning Electron Microscopy, Rutherford Backscattering Spectrometry and X-Ray Diffraction), it was possible to successfully separate the effects of strain and composition on the frequency of the InxGa1-xN A1 (LO) phonon. Consequently, the deformation potentials, concerning the A1 (LO) phonon, were determined, and the phonon frequency dependency on the alloy composition was established. The relaxation process of the InxGa1-xN lattice, along the growth direction, was studied by the use of Raman spectroscopy on a set of samples that had suffered a chemically controlled etching. This study enabled to consolidate the interpretation of all the experimental results concerning the frequency and spectral shape of A1 (LO) phonon. Apart of the study of lattice dynamics, and since this study required that absorption and emission energies related to electronic transitions were identified, the emission at 1.88 eV, on a partially relaxed sample, was observed and characterized. Finally, a study was developed aiming to evaluate the receptivity, of the InxGa1-xN matrix, to the incorporation, by means of ionic implantation, of rareearth ions, in particular of Er3+. Therefore, luminescence at ~1.5 μm, linked to the intraionic transition of excited state (4I13/2 ) to fundamental state ( 4I15/2), was also studied. Results have shown that ion incorporation by an implantation process is not the most suitable for InxGa1-xN lattice.

En utilisant la méthode des ondes planes augmentées avec linéarisation (FP-LAPW), nous avons étudié les propriétés structurales et électroniques des alliages ternaires AlxGa1-xN, InxGa1-xN et InxAl1-xN cubiques et wurtzites. Nous avons utilisé les structures de Landau-Lifshitz, la chalcopyrite et la luzonite, pour modéliser les alliages cubiques, et une super-cellule de 32 atomes pour les alliages wurtzites. L'analyse de nos résultats en comparaison avec d'autres calculs montre une forte dépendance du facteur de courbure avec le paramètre du réseau. On remarque aussi que les résultats sont influencés par le model structural utilisé pour les alliages ternaires. Finalement, nous avons étudié le comportement de l'énergie du gap des binaires et des ternaires dans la structure wurtzite sous l'effet de la pression. Nous en avons déduit le comportement des coefficients de pression avec la concentration, et la variation du facteur de courbure du gap avec la pression.

碩士
國立臺灣大學
物理研究所
95
This thesis focuses on electron transport properties of InxGa1-xN thin films. The transport measurements were performed on InxGa1-xN thin films over a wide temperature range (12 K< T < 315 K). The four independent van der Pauw measurements, each with 90∘rotation of contact configuration to measure the resistance of , were used. These samples show a tendency from semiconductor to metal with increasing x of InxGa1-xN , indicating InN electron transport properties are better than GaN. The resistivity of InN was best fitted with Block T^5 law. This supports the high In composition films can be considered as degenerate electron system in which the Fermi level is much higher than conduction band over the whole temperature range. Taking this characteristic into consideration, in this thesis the phenomenon of the electron-acoustic phonon interactions were investigated under the low temperature condition.

碩士
國立臺灣大學
物理研究所
93
This thesis focuses on electron transport properties in InxGa1−xN (x =1, 0.98, 0.92, 0.8, 0.7) thin films. We have performed transport measurements on InxGa1−xN thin films over a wide temperature range. We observed that within experimental error, the carrier densities are temperature independent. Besides, the resistivities, combined with the carrier densities, show a tendency of transition from metal to semiconductor with increasing Ga composition. The calculated mobility shows that for metallic like samples (InxGa1−xN with x ≥0.92), the dominant scattering mechanism is the imperfection scattering over the whole temperature range. We also showed that Bloch T5 curves fit very well the resistivities of samples InxGa1−xN with x =1, 0.98, 0.92, once again supporting that very high In composition InxGa1−xN films can be considered as degenerate electron systems in which the Fermi level is much higher than conduction-band bottom over the whole measurement range.

碩士
國立臺灣海洋大學
光電科學研究所
94
We have performed the polarization modulation near-field scanning optical microscopy (PM-NSOM) measurements to investigate the correlation between crystalline and optical properties of InGaN epilayers and crystalline quality of In-rich InGaN epilayers. The PM-NSOM results show the nanoscale domain-like structures which exhibit good correspondence to the morphological images by SEM measurement. It is found the In-rich regions formed at the periphery of the hexagonal pits. These In-rich regions show good crystallinity and high recombination efficiency. We point out that the combination of PM-NSOM and NSOM-PL is a powerful tool for investigating the correspondence between the local morphology and the optical properties of the nanostructures. The crystalline properties of In-rich InGaN films with Ga concentration varying from 0% to over 30% were investigated by PM-NSOM measurements. PM-NSOM measurements showed that the crystallinity of InGaN films were strongly dependence on the Ga concentration. The average crystallinity of InGaN film was found to decrease with the increase in Ga concentration of InGaN films. On the other hand, the RMS crystallinity exhibited a different dependence on the Ga concentration for the In-Rich InGaN films. The RMS crystallinity of InGaN films first decreased with the increasing Ga concentration, reached a minimum for the InGaN film with 8% Ga concentration, and then increased again with increasing Ga concentration. Surprisingly, the RMS crystallinity of InGaN films shows the same trend in the dependence of PL intensity on the Ga concentration in InGaN films. It was concluded that for the InGaN films with different Ga content grown at the same temperature, the RMS crystallinity of the epifilms accounts for PL emission efficiency of the epilayers.

博士
國立交通大學
電子物理系所
98
In this dissertation, the use of preheating ammonia installation can be used to increase the thermal decomposition efficiency of ammonia, we have demonstrated that the entire composition of InxGa1-xN epilayers prepared by MOCVD can be achieved merely by varying the growth temperature and In vapor mole fraction. First, the In solid composition, as anticipated, was increased from 0.14 to 0.40 as the growth temperature decreased from 750 to 650 oC, which corresponds to a wavelength can be extends to the 738 nm in the deep red region with linewidth 180 meV. Further, as input In vapor mole fraction raise to 73 %, we could estimate that the In solid composition of the InxG1-xN films increases to 0.44, which corresponds to a wavelength range extend to near infrared 950 nm with linewidth 235 meV. Therefore, we have surmounted the technique bottleneck of the absence of entire composition of InGaN epilayers, especially the emission wavelength 650-1100 nm. For samples grown at temperature > 700 oC, separated by about 500 meV, two emission peaks are observable. The corresponding emission peaks, namely high and low emission peaks, are shift from 2.94 to 2.58 eV and from 2.44 to 2.07 as the growth temperature decrease from 750 to 700 oC. The high peak energy originates from strained layer closer to GaN buffer and low energy from relaxed layer near the surface, as revealed by the results of high-resolution x-ray reciprocal space mapping (RSM) and cathodoluminescence (CL) measurements. For samples grown at temperature < 700 oC, high In content epilayers having a large lattice mismatch with under GaN buffer layer, the nearly absence of strained layer resulting in the feature of single emission peaks in both PL and CL spectra. In order to further extend the wavelength of the InGaN epilayer, we grew the InGaN sample at a growth temperature of 650 oC, in an attempt to investigate the dependence of InGaN solid composition on input In reactant flow rate. For the In solid composition, we thought that too high the TMIn flow rate will lead to decrease of In concentration solid, unfavorable to the high In content InGaN growth. Besides, we also reveals that the 14-K photoluminescence peak energy of InGaN epilayers exhibit a wide emission tunability from 2.75 to 1.29 eV, covering a wavelength ranges from blue, green, red and even reaches infrared 960 nm spectrum region. It shown that the bowing parameter of b ~ 2.3 eV for our results and the literature data for the band gap of InxGa1-xN over the entire composition. Our observation provides conclusive evidence that the InxGa1-xN epilayers exhibits a larger Stokes shift, showing that the alloy’s inhomogeneity.

碩士
國立交通大學
電子物理系
88
Abstract The InxGa1-xN:Si / GaN heterostructure grown on the (0001) sapphire substrates by metalorganic chemical vapor phase epitaxy (MOVPE) has been investigated by AFM, PL, and PLE. We have observed clearly the spatial fluctuation of In at high In concentration and the transitions from the InxGa1-xN band-edge. The yellow emission as resulted from the photoexcited carriers above the GaN A exciton a has also been proved. We also studied the isoelectronic As-doping effects in GaN films grown by MOVPE. Two series of As-doped GaN, one grown at various temperatures (from 1050 to 800℃) and the other under different tertiary butylarsine (TBA) flow rates (from 0 to 100 sccm) were investigated by PL, PLE, Raman and Hall measurements. High mobility can be obtained even at a temperature of 950℃ and the low background concentration of approximately 5×1017 cm-3 at 900℃. The narrow linewidths of PL and Raman signals are observed by increasing the As-incorporation The As-doped induced strain along the c-axis (the large A1(LO) frequency shifts) easily. Our results suggest that the use of As-doping is helpful to the growth of GaN at low temperature and expanded the growth temperature window.

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.

碩士
長庚大學
光電工程研究所
99
Abstract Since the 21th century, the requisite energy increase continually. Use massively of fossil fuels caused that our earth to be faced with Climatic change, Lack of energy and natural resourse , and Environmental pollution issues. so we have to develop safe and neat renewable energy sources. In the III-V compound semiconductor, the bandgap of InxGa1-xN can change from 0.7eV to 3.4eV, It can be use effectively to absorb the wide solar spectrum, and to fabricate the solar cells more efficient . In the paper, we use the In0.27Ga0.73N MQW solar cells to be our bottom cells and use In0.19Ga0.81N solar cells to be our top cells, and to improve the photo current of bottom cells by design the structure of bottom cell. Finally, we combine top cells with bottom cells to be cascade MQW solar cells by series way and parallel way. In our experiments the efficiency of series way and parallel way which bottom cells with Au reflective layer and stick by Ag epoxy direct are 0.66%&0.63%, the efficiency of series way and parallel way which bottom cells with Al reflective layer and stick by Ag epoxy direct are 0.92%&0.96%, the efficiency of series way and parallel way which bottom cells without reflective layer and stick by Ag epoxy direct are 0.8%&0.83%, the efficiency of series way and parallel way which bottom cells use flip chip method with Au submount are 0.8%&0.83%, and the efficiency of series way and parallel way which bottom cells use flip chip method with Al submount to reach 1.14%&0.7%.

碩士
國立臺灣大學
光電工程學研究所
100
This thesis studied silicon based InxGa1−xN multi-junction tandem solar cells. To investigate the the multi-junction tandem solar cells, we developed a simulation model by using 1D Poisson and drift-diffusion solver with an assumed effective tunneling layer. As we know, if we want to calculate the current-voltage curve, we have to calculate the tunneling probability between the heavily doped n layer and p layer. However the 1D Poisson and drift-diffusion solver does not include the function to handle the tunneling current. Therefore, we assume that there is a virtual tunneling layer between the heavily doped n layer and p layer by changing the tunneling layer potential bandgap, recombination coefficient to explain influences of defect state level to the tunneling probability. Besides, we propose the concept of electron/hole blocking layer for the photovoltaic. We discusses the effect of electron/hole blocking layer on the photovoltaic performance of the single junction solar cells. The study shows that with a pure electron blocking on the p-type doping Si and a pure hole blocking layer on n-type doing, it is possible to enhance the open circuit voltage and short circuit current. Therefore, the Ga2O3 and TiO2 materials are chosen as the electron and hole blocking layer. The result shows that the open circuit voltage increases from 0.65 eV to 0.80 eV, and the short circuit current increases from 35.1 mA/cm2 to 35.9 mA/cm2 , where the power efficiency can increase from 21.9 % to 27.6 %. Finally, we use the above studies to investigate the performance of the silicon based InxGa1−xN multi-junction tandem solar cells. We find the optimized condition of the In composition and layer thickness of crystalline Si for the highest efficiency double-junction and triple-junction solar cells. After that, we analyzes the polarization effect on of the silicon based InxGa1−xN tandem junction solar cells with different top layer. Under the different InxGa1−xN growth face, the polarization charge at the heterojunction will induce different polarization field which can reduce or enhance the ability of the photo-generated holes collection. Making a great difference to the efficiency of the InxGa1−xN tandem junction solar cell. In our simulation, the graded InxGa1−xN tandem junction solar cells growth on the N-face can be the electron blocking layer which enhance the performance of the solar cells. The efficiency increases from 29.6% to 33.4%.

碩士
國立臺灣科技大學
化學工程系
99
We demonstrated the catalytic growth of InxGa1−xN nanowire (NW) arrays (0.06≦x≦0.17) on silicon substrate using metal-organic chemical vapor deposition technique. X-ray diffraction characterization confirmed that the InxGa1−xN NWs are single phase wurtzite structure without any binary phase. Transmission electron microscopy results showed that the single crystalline NWs were grown in (100) direction and dislocation-free. Photoluminescence results showed that the band gap of InxGa1−xN NW can be modulated down to the visible spectrum region depending on the ratio of In in the nanowires which can be modulated by varying the growth conditions. Our results suggest an approach to fabricate single phase, large area NW on silicon with standard MOCVD method, which offers an opportunity to transfer the production from research to industrial scale.

碩士
中原大學
應用物理研究所
91
CdxZn1-xTe epilayers were grown on the GaAs(001) substrates by the molecular beam epitaxy. The optical properties of the epilayers were studied by the reflectance (R) and photoluminescence (PL) measurements. The energy gaps were found to decrease with the Cd concentration. The exciton activation energy, which is determined from the integrated PL intensity versus temperature plot, shows a decrease with the Cd composition. Temperature dependence of the energy gap, measured by the PL spectra, was fitted by the Varshni's and the O'Donnell's relation. Good fits were obtained with both relations for the samples with small Cd concentration. However, for the Cd0.582Zn0.418Te epilayer, the O'Donnell's fit shows more reasonable trend. In addition to the CdxZn1-xTe epilayers, the optical properties of the InxGa1-xN epilayers were investigated by using the PL, R and transmission (T) techniques. The InxGa1-xN epilayers with x = 0, 0.08, 0.10 and 0.15 were grown by metal organic chemical vapor deposition on the sapphire substrate. Sharp PL line-shape was observed. Band-tailing model was employed to explain the reason why the PL peak exhibits energy blue-shift and then red-shift as temperature increases. The effect of Indium mole fraction on the exciton activation energy and the temperature dependent PL line-width were obtained. A preheating of the sapphire substrate at 1300 oC was proved to be essential for the improvement of the epilayer’s optical quality.

碩士
國立清華大學
工程與系統科學系
90
We apply X-ray diffraction to characterize the structure of InxGa1-xN-GaN MQWs and study the effect of thermal-annealing from the structural point of view. Surface-normal (00.2) and (00.4) diffraction profiles were collected and analyzed by numerically fitting with the dynamical theory of X-ray diffraction. In our sample system, the measured value of molar fraction x of indium composition in InxGa1-xN layers is 0.17 (±0.01), which has been verified by solving a modified relation of elasticity, given by us for the first time, valid to the strained InxGa1-xN-GaN bilayer. According to mesh scans around the zeroth-order of (00.2) super-lattice reflection of sample at different post-annealing temperatures, we observed an asymmetric tendency of the diffraction contours evolving to two peaks. This observation implies that two distinct values of indium composition are well separated in the 1000°C-annealed MQWs sample. The proposed interpretation was supported by X-ray reflectivity data and consistent with the splitting of emission peak shown in the PL spectrum. From the photoelectronic point of view, according to the blue shift and varying of FWHM observed in PL and XEOL spectra, we indicate that the interface roughness is an important factor in the formation of an extra and larger bandgap in addition to the ordinary bandgap of quantum wells. Thermal activation initiated the interdiffusion of In and Ga ions at rough interfaces. High-temperature annealing would promote the inter-diffuse process and then diffusion layers at interface were gradually formed. Sharper interfaces were achievable if sample annealed further at high temperatures; even though, fully coherent strains were still remained in the 1000°C-annealed sample. The compositional variation at interface turned out to be a certain subband layer of quantum wells, because the as-grown roughness transformed into smooth diffusion layers by annealing.

碩士
國立臺灣大學
物理研究所
94
In this thesis we report a detailed study on the structural and optical properties of InGaN alloys. Quite interesting results have been obtained from our studies which would be very useful for our understanding and application of these materials. Our investigation is concentrated on the origin of Stokes shift in InxGa1-xN alloys with 0≦x≦1. The fundamental band gaps of InGaN alloys, depending on the indium concentration, can cover from near-ultraviolet to infrared, as a result this alloy system is capable of generating many optoelectronic devices. Based on the absorption and luminescence spectra, it clearly shows that there exists a large Stokes shift in InGaN alloys. Our experimental results together with the previous reports lead to a complete picture of the Stokes shift covering 0≦x≦1. Combining with the measurements of scanning electron microscope, cathodoluminescence, energy dispersive spectroscopy, and photoluminescence, we establish that the origin of the Stokes shift in InGaN ternary compound arises from alloy composition fluctuations.

碩士
國立交通大學
電子物理系所
107
InxGa1-xN (0