Directional crystallization of CdHgTe in microgravity conditions

Abstract

Two experiments on crystallization of Cd 0.22Hg 0.78Te mixed crystals from the liquid phase were performed on the Salyut 6 Space Laboratory. The rates of growth varied in time from 2 mm/h to 50 mm/h. The properties of the crystals were found to be strongly dependent on the growth rate. For slow rates of crystallization, diffusion-controlled growth took place and homogeneous material was obtained. For rates higher than 3 mm/h spontaneous crystallization began, creating cavities which gave rise to further inhomogeneities in the material. In this paper the crystallization process is described and data on some basic structural and electrical properties of the space-grown crystals are presented together with the results of composition and surface morphology studies. A new effect, the formation of a surface layer about 30 μm thick and differing in composition from the bulk material, was discovered. The electrical properties of the crystal showed no apparent effect of zero-gravity conditions on deviations from stoichiometry.