Thermal behavior of noncrystalline sputtered films in the system GeTe

Abstract

As part of a systematic study of vapor deposited noncrystalline solid (VDNCS) sputtered films in the GeTe system, this paper reports on the thermal behavior of these films. Heating experiments were conducted on samples of various compositions throughout the NCS forming region which extends from pure Ge to at least 95 at.% Te. The crystallization temperatures of the films have been shown to be highly reproducible and sensitive to the particular NCS structure. At compositions from 70 to 95 at. % Te and at 30 at. % Te two stage crystallization was observed, in which the Te phase and Ge phase, respectively, crystallized first, followed in both cases, by crystallization of GeTe. All other compositions showed single stage crystallization in which the two phases, either GeTe + Te or GeTe + Ge, crystallized simultaneously. The possible existence of non-uniform structure in the films is indicated in the data on two stage crystallization. The relation between the crystallization temperature and the degree of disorder, or structure, of the VDNCS films is discussed with emphasis on both the composition and conditions of preparation of the films. The relevance of the current results to memory switch device research is noted.