Investigação das propriedades ópticas, morfológicas e elétricas da heterojunção SnO2: Ce3+/ GaAs
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Data
2016-03-03
Autores
Machado, Diego Henrique de Oliveira [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Este trabalho apresenta o desenvolvimento e algumas conclusões do estudo da heterojunção de filmes finos de SnO2 e GaAs. Os filmes de SnO2, dopados com Ce3+, foram depositados a partir do método sol-gel usando as técnicas de dip e spin coating; os filmes de GaAs foram depositados por evaporação resistiva e por sputtering. As heterojunçõesforam constituídas de filmes de SnO2 sobre filmes de GaAs, e filmes de GaAs sobre filmes de SnO2. Foram investigadas as propriedades ópticas, estruturais, morfológicas e elétricas de filmes finos constituintes das heterojunções e também a influência do dopante Ce3+. Entre os experimentos realizados estão: transmitância óptica, difração de raios X, microscopia eletrônica de varredura (MEV), microscopia óptica, microscopia de força atômica (AFM), fotoluminescência e medidas elétricas na presença de excitações com diferentes fontes de luz monocromáticas (quarto harmônico do laser Nd:YAG (266nm), laser He-Ne (628nm), LED InGaN (450nm)). Entre as principais conclusões, verificou-se: 1) em algumas situações, condutividade independente da temperatura, sugerindo a participação de um gás de elétrons bidimensional (2DEG) na interface SnO2/GaAs; 2) o tamanho dos cristalitos, calculado a partir das análises de difração de raios X, fornece valores da ordem de 10nm tanto para filmes de SnO2 como para filmes de GaAs; 3) a energia de bandgap, avaliada com base em dados de medidas de absorbância, fornece um valor máximo de 3,6 eV para filmes de dióxido de estanho e 1,6eV para filmes de GaAs; 4) MEV e microscopia óptica de para filmes de GaAs (depositado por evaporação resistiva e sputtering) apresentam sua superfície heterogênea, com partículas de variados tamanhos. Além disso, a aderência de filmes de SnO2 sobre filmes de GaAs está relacionada com a técnica utilizada para depositar os filmes da camada de base, o melhor resultado foi obtido quando a camada é a de GaAs depositado por evaporação resistiva. Isto foi verificado utilizando microscopia de força atômica, onde ficou evidente que filmes de GaAs depositado por evaporação resistiva possuem grandes aglomerados enquanto filmes depositados por sputtering possuem uma superfície com material distribuído de maneira uniforme. Também foram realizadas medidas de fotoluminescência com excitação de um laser de Kr+ sintonizado na linha de 350nm e também utilizando um laser de He-Cd na linha de 325nm, tanto em filmes como em pastilhas de SnO2 dopado com 1at% Ce3+e também em filmes da heterojunção SnO2:Ce3+/GaAs, sendo observadas pequenas bandas características do Ce3+.
The aim of this work is to present the development and the main conclusions, related the investigation of thin film SnO2/GaAs heterojunction. Ce3+- doped SnO2 thin films were deposited by the sol-gel-dip and -spin coating techniques, whereas GaAs films were deposited by resistive evaporation and sputtering. Heterojunctions were deposited by SnO2 layer growth on top of GaAs film, and in the opposite order: GaAs on top of SnO2. Optical, structural, morphologic and electrical properties of heterojunction films were investigated, as well as the influence of Ce-doping in these measurements. Experiments carried out include: optical transmission, X-ray diffraction, scanning electron microscopy (SEM), optical microscopy, atomic force microscopy (AFM), photoluminescence and electrical measurements under optical excitation. In this last case the excitation sources are monochromatic light from the fourth harmonic of a Nd:YAG laser (266nm), a He-Ne laser (628nm) and a InGaN LED (450nm). Among the main conclusions, it was verified that: 1) in some situations, a temperature independent electrical resistivity was observed and attributed to the possible formation of a two-dimensional electron gas (2DEG) at SnO2/GaAs interface; 2) crystallite size was calculated from X-ray diffraction data, being about 10 nm either for SnO2 films as GaAs films; 3) bandgap energy, evaluated from absorbance data yield a maximum value of about 3.6eV for tin dioxide and 1.6eV for GaAs films; 4) SEM images, obtained for GaAs thin films deposited by resistive evaporation and for the heterojunction SnO2/GaAs, and optical microscopy, for sputtering deposited GaAs films and heterojunction samples, show that GaAs films present an heterogeneous surface, with particles of several distinct sizes. Besides, the adherence of SnO2 films on the GaAs layer is related to the used technique for depositing the base layer, being better in the case of resistive evaporation deposited GaAs. This was verified by atomic force microscopy, where it was evidenced that resistive evaporation deposited GaAs films present large agglomerates whereas sputtering deposited films present a surface with more uniformly distributed material. Photoluminescence data was also obtained with excitation by a Kr+ laser tuned at 350nm as well as a He-Cd laser at 325nm, either in Ce 1at% doped SnO2 pellets as SnO2:Ce3+/GaAs heterojunction, being observed small bands, characteristic of Ce3+.
The aim of this work is to present the development and the main conclusions, related the investigation of thin film SnO2/GaAs heterojunction. Ce3+- doped SnO2 thin films were deposited by the sol-gel-dip and -spin coating techniques, whereas GaAs films were deposited by resistive evaporation and sputtering. Heterojunctions were deposited by SnO2 layer growth on top of GaAs film, and in the opposite order: GaAs on top of SnO2. Optical, structural, morphologic and electrical properties of heterojunction films were investigated, as well as the influence of Ce-doping in these measurements. Experiments carried out include: optical transmission, X-ray diffraction, scanning electron microscopy (SEM), optical microscopy, atomic force microscopy (AFM), photoluminescence and electrical measurements under optical excitation. In this last case the excitation sources are monochromatic light from the fourth harmonic of a Nd:YAG laser (266nm), a He-Ne laser (628nm) and a InGaN LED (450nm). Among the main conclusions, it was verified that: 1) in some situations, a temperature independent electrical resistivity was observed and attributed to the possible formation of a two-dimensional electron gas (2DEG) at SnO2/GaAs interface; 2) crystallite size was calculated from X-ray diffraction data, being about 10 nm either for SnO2 films as GaAs films; 3) bandgap energy, evaluated from absorbance data yield a maximum value of about 3.6eV for tin dioxide and 1.6eV for GaAs films; 4) SEM images, obtained for GaAs thin films deposited by resistive evaporation and for the heterojunction SnO2/GaAs, and optical microscopy, for sputtering deposited GaAs films and heterojunction samples, show that GaAs films present an heterogeneous surface, with particles of several distinct sizes. Besides, the adherence of SnO2 films on the GaAs layer is related to the used technique for depositing the base layer, being better in the case of resistive evaporation deposited GaAs. This was verified by atomic force microscopy, where it was evidenced that resistive evaporation deposited GaAs films present large agglomerates whereas sputtering deposited films present a surface with more uniformly distributed material. Photoluminescence data was also obtained with excitation by a Kr+ laser tuned at 350nm as well as a He-Cd laser at 325nm, either in Ce 1at% doped SnO2 pellets as SnO2:Ce3+/GaAs heterojunction, being observed small bands, characteristic of Ce3+.
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Palavras-chave
Dióxido de estanho, Terra-rara, Cério, Arseneto de gálio, Heterojunção, Tin dioxide, Rare-earth, Cerium, Gallium arsenide, Heterojunction