PLASMA-ENHANCED CVD OF AMORPHOUS GEXS1-X AND GEXSE1-X FILMS

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 GexS1-x and GexSe1-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 Ge0.66Se0.34) and Se-rich deposits (maximum Ge0.23Se0.77). 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.