Improved Techniques for the Growth of High Quality Cadmium Telluride Crystals

摘要

This report summarizes two years' work as part of a multiyear program on improved techniques for the growth of high quality cadmium telluride crystals and represents one of the most comprehensive studies of melt growth and defect characterization in CdTe reported to date. Extensive melt growth studied were carried out using the vertical Bridgman method. Growth parameters were systematically varied in order to determine the influence of seed orientation, thermal environment, and growth rate on crystal quality. Growth interface shapes were revealed using autoradiographic dopant tracing methods. Melt thermal profiling was also carried out to further evaluate growth interface shapes. Controlled convex growth interface shapes were generated by using the heat exchanger method. By this means some improvement in grain structure of the typically polycrystalline boules was accomplished. Low frequency melt vibrations during growth were also observed to improve grain structure and reduce dislocation density. Extensive defect characterization was also carried out using chemical etching methods, and later, synchrotron x-ray topography. Comparative studies of a broad selection of commercial CdTe substrates was carried out, and extensive defect structure was observed in all cases. Reduced dislocation densities and defect structures were accomplished using both low amplitude melt vibrations and doping with In 113. In the second case, solution hardening was assumed to be the mechanism responsible. For the case of melt vibration, the mechanism is not yet understood.