Structure and epitaxy of evaporated cadmium selenide films

Abstract

Cadmium selendide films were thermally evaporated onto Corning 7059 glass and (110) KC1 single crystals at temperatures between 25° and 300°C. Films between 0.05 and 1.0 μm thick were deposited at rates between 1.7 and 32 Å/s and their microstructure investigated by transmission electron microscopy, reflection electron diffraction, and x-ray diffraction. The würtzite-hexagonal phase of CdSe was always observed at substrate temperatures up to 200°C but, in the case of KCl, it co-existed with the sphalerite-cubic phase. The crystallite size and the degree of ordering of CdSe increased with increasing substrate temperature and film thickness. For example, the ratio of x-ray intensities from (00.2) and (10.0) planes in films deposited on glass substrates increased by more than two orders of magnitude as film thickness increased from 0.05 to 1 μm. At glass substrate temperatures greater than 200°C, Cd3Se4O11 was also formed. The structure of films deposited on KCl changed from a polycrystalline mixture of cubic and hexagonal phases to a single crystalline (111) cubic phase with increasing thickness. This effect can be attributed to recrystallization caused by thermal stresses induced by the difference in thermal expansion of film and substrate.