Gravitational influences on the liquid-state homogenization and solidification of aluminum antimonide

Abstract

Although the III-V compound aluminum antimonide (AlSb) shows promise as a highly efficient solar cell material, its semiconducting properties have not been exploited for device development due to difficulties in synthesizing a homogeneous stoichiometric compound and growing single crystals by conventional techniques. Liquid-state homogenization analysis, which examines the relative influence of gravitational flowvs interatomic diffusion, suggested that the microscopic inhomogeneities observed in commercial polycrystalline samples could be due to gravitational influences caused by large density differences between Al- and Sb-rich phases in earth based melts. Several liquid-state homogenization and solidification experiments performed on earth and a similar experiment performed during the Apollo-Soyuz Test Project mission in July 1975 verify this theoretical conclusion. Using comparative characterization techniques for identically processed low and one gravity samples of commercially available AlSb, this paper reports on gravitational influences, such as density driven convection or sedimentation, that cause microscopic phase separation and nonequilibrium conditions to exist in earth based melts of AlSb. The reported experiments have, likewise, shown that such phase separations can be greatly reduced in a low gravity environment and lead to major improvements in microscopic homogeneity of the re crystallized material.