The Investigation of Zinc Selenide Buffer Layers for Reduction of Defects in the Heteroepitaxial Growth of Gallium Arsenide on Silicon

The present study was initiated to investigate the use of zinc selenide as a buffer layer in the heteroepitaxy of gallium arsenide on silicon. ZnSe and GaAs single crystal films were grown on silicon substrates using the Washington State University/Tri-Cities metalorganic chemical vapor deposition reactor. Procedures were developed to first optimize the ZnSe and then the GaAs film quality. Surface morphology and x-ray diffraction guided the development of ZnSe films to achieve (100) crystal orientation films. A two-rate growth procedure was adopted where the initiation step involved growing 500A at approximately 1A/sec at 450 ^circC followed by growth at 5A/sec. Film quality of the GaAs layers was evaluated by various techniques. Scanning electron microscopy examined the surface morphology of the films. Electrochemical capacitance -voltage profiling gave insight into electrical and defect structure. Etch-pit density studies and transmission electron microscopy evaluated the defect density and structure. Eventually, films were adherent, specular, and relatively smooth. Minority carrier diffusion lengths in the GaAs films were studied using photoresponse analysis of semi-transparent Schottky diodes. Schottky barriers were fabricated by vacuum depositing a thin layer of aluminum onto the GaAs films. The minority carrier diffusion length modeled for these films showed gradual improvement with development from an initial value of L = 0.00 μm to 0.30 μm for the best 3.0 μm films. The development of a low temperature GaAs cap layer on the ZnSe followed by higher temperature GaAs growth was responsible for improvements in L, the diffusion length.