Pressure-dependent nanohetero-epitaxy of cadmium telluride on silicon(100) and SOI substrates using the close-spaced sublimation technique
CdTe is an ideal II-VI semiconductor compound with a direct bandgap energy of 1.53 eV used in solar cells and infrared detector applications . The National Renewable Energy Laboratory (NREL) reported that cadmium telluride (CdTe) thin films solar cells have achieved efficiency of 16.5% and with potential for improvement up to the theoretical value of 29% . The close-spaced sublimation (CSS) method used for solar cell CdTe growth is being tested for selective CdTe nanoheteroepitaxial growth because the CSS method is cost efficient compared to the molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) methods. High quality films are identified by SEM based on the CdTe grain size, selectivity, uniformity of the selective CdTe deposition, and appearance of CdTe grain surface. The goal of this study is to obtain selective growth that result in faceted grains with smooth flat surfaces. Previous studies by A. Escobedo and A. Diaz were used as a basis for the experiments conducted in this study. The CSS source and substrate temperatures resulting in selective growth are based on successful results by Escobedo and Diaz. The helium gas pressure was varied in this thesis work as a way to vary the grain size. Based on a recent study by Major et al., they were successful in reducing the CdTe grain size by reducing the gas pressure within the CSS reactor . Therefore, this study focused mainly on the variation of the helium gas pressure as a way to achieve selective growth and to obtain a uniform CdTe pattern. Six variations of CdTe deposition studies are conducted in order to examine the effects of helium gas pressure, source temperature, substrate temperature, deposition time, and pattern size on the Si(100) and SOI(100) substrates using the CSS technique. Bhat and Zhang performed a study for selective CdTe deposition using the MOVPE system . Zubia has also studied the GaAs deposition on SOI(100) substrates using the MOVPE system. However, this is the first time 100 nm patterned SOI(100) substrates are used for selective CdTe growth using the CSS method. The scanning electron microscopy (SEM) and x-ray diffraction (XRD) are used to analyze the quality of the film.
Electrical engineering|Condensed matter physics|Materials science
See Tao, Hoong Yan, "Pressure-dependent nanohetero-epitaxy of cadmium telluride on silicon(100) and SOI substrates using the close-spaced sublimation technique" (2011). ETD Collection for University of Texas, El Paso. AAI1498321.