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

X-ray photoelectron spectroscopy experiments were performed on as-depo sited evaporated a-GexSe100-x compound films, with x ranging from 20 t o 50 at.%, in order to investigate the changes in the core level and v alence band electron distribution as a function of composition. The re sults are interpreted in terms of short-range ordering, taking the sto ichiometric a-GeSe2 compound as a reference. The valence band spectra are compared to theoretical predictions and discussed in relation to o ptical data obtained on the same samples. It is shown that 4:2 coordin ation is maintained over the whole composition range, and that chemica lly ordered structural units are favoured in all cases.