Anneal Induced Changes in Amorphous Semiconductor Multilayers

Abstract

ABSTRACTWe have prepared, heat treated and characterized various amorphous semiconductor periodic multilayers and ultrathin films. These were prepared by several vapor deposition techniques at substrate temperatures ranging from 25°C to 300°C and possessed periodicities from 22 to 400Å. Films were subjected to isochronal thermal treatments at progressively higher temperatures. Two effects were observed: enhanced diffusion and retarded crystallization. Interdiffusion, at rates which are many orders of magnitude higher than those anticipated from crystalline data, was observed in a-Si/a-Ge multilayers. Crystallization of germanium, the more readily crystallized member of the couple, is retarded; the extent depends on the thickness of the layer. The thinner the layer, the greater the retardation. Where intermixing is thermodynamically unfavorable as in a-Si/a-SiNx or a-Ge/a-SiNx multilayers, and ultrathin germanium layers on SiO2, interdiffusion does not occur, however, crystallization of silicon or germanium is again substantially retarded.