Microscopic and spectroscopic analysis of cadmium telluride
Cadmium telluride (CdTe) remains one of the materials of interest in the fabrication of photovoltaic cells and infrared devices, mainly because of its suitable crystal structure as well as of its small, direct bandgap of 1.5 eV. Since development of such devices requires a high quality and low defect material, the goal of this study is to microscopically and spectroscopically examine not only crystallinity, but also the induced stress in the material due to the effect of substrate orientation. This information is valuable if optimization of sample growth conditions is envisioned. Prior to CdTe deposition by close-spaced sublimation (CSS), Si (111) and (211) substrates were patterned using photolithography and dry etching to create 500 nm to 1 m pillars. Scanning electron microscopy (SEM) images besides demonstrating uniform, selective growth of polycrystalline CdTe, reveal fewer defects and less twin-microcrystallite formation if Si (211) is used. Crystallinity of the samples was investigated by Fourier transform infrared absorption and Raman spectroscopies. The far-infrared transmission data show the presence of transverse optical (TO) and surface optical (SO) modes, the latter being direct evidence of confinement in such a material. Qualitative identification of the induced stress in the samples was achieved by performing confocal Raman mapping microscopy on their surfaces. These investigations indicate that the deposited material is under compressive stress, largely because of the high lattice mismatch between CdTe and the Si substrate. As high quality materials with excellent ordered structure are needed for developing photovoltaic devices, the results of this research demonstrate the importance of detailed, comprehensive analysis in optimizing and improving CdTe characteristics.
Salazar, Jessica G, "Microscopic and spectroscopic analysis of cadmium telluride" (2015). ETD Collection for University of Texas, El Paso. AAI1591991.