Plasma-enhanced C.V.D. of amorphous GexS1-x, and GexSe1-x films

We describe plasma-enhanced chemical vapour deposition for decomposing a mixture of two gaseous hydrides, GeH 4 and H 2 S or H 2 Se, to yield layers of amorphous Ge x S 1-x and Ge x Se 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 0.66 Se 0.34 ) and Se-rich deposits (maximum Ge 0.23 Se 0.77 ). The incorporation of sulfur was less effective: maximum 57 at.% S in Ge-S layers (GeH 4 /H 2 S=1/96 and p=0.1 mbar) i.e. less than the stoichiometric composition GeS 2 . 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