Plasma-enhanced C.V.D. of amorphous Ge_xS_1-x, and Ge_xSe_1-x films

Abstract
We describe plasma-enhanced chemical vapour deposition for decomposing a mixture of two gaseous hydrides, GeH₄ and H₂S or H₂Se, to yield layers of amorphous Ge_xS_1-x and Ge_xSe_1-x. We discuss the influence of the gas ratios and the deposition conditions (pressure, rf power input) on the chemical composition and homogeneity of the films. For Ge-Se samples, the composition varied between Ge-rich (typically Ge_0.66Se_0.34) and Se-rich deposits (maximum Ge_0.23Se_0.77). The incorporation of sulfur was less effective : maximum 57 at.% S in Ge-S layers (GeH₄/H₂S = 1/96 and p = 0.1 mbar) i.e. less than the stoichiometric composition GeS₂. Information concerning the structure of as-deposited Ge-S and Ge-Se layers was obtained from infrared and Raman spectroscopy. Ge-rich films of both Ge-S and Ge-Se were unstable in air and showed in their IR spectra broad absorption bands of Ge-O vibrations, increasing in intensity when keeping them in air for a long time.