STUDIES OF SHORT-RANGE ORDER IN AMORPHOUS GEXSE100-X COMPOUNDS BY X-RAY PHOTOELECTRON-SPECTROSCOPY

X-ray photoelectron spectroscopy experiments were performed on as-deposited evaporated a-GexSe100-x compound films, with x ranging from 20 to 50 at.%, in order to investigate the changes in the core level and valence band electron distribution as a function of composition. The results are interpreted in terms of short-range ordering, taking the stoichiometric a-GeSe2 compound as a reference. The valence band spectra are compared to theoretical predictions and discussed in relation to optical data obtained on the same samples. It is shown that 4:2 coordination is maintained over the whole composition range, and that chemically ordered structural units are favoured in all cases.