Physical characterization of amorphous GeSe2 films

AC conductivity, photodarkening and electron spin resonance measurements are carried out on amorphous GeSe2 films. The AC conductivity is measured as a function of frequency and temperature. The AC conduction mechanism of the studied films is interpreted via single electron transfer between the C−1(C+3) and C0 centers. The photodarkening is induced with He–Ne laser and observed as transmission and reflection changes through 1.02 μm thick film. Both reversible and irreversible processes are detected with these measurements. The reversible process is induced by defects located in energy at the band edge. The presence of these defects is confirmed by the blue shift of the band edge and the restoration of the initial optical gap value by annealing. On the other hand, the irreversible process results from defects situated in energy into the band tails. These defects cause a considerable additional absorption below the band edge and a remarkable decrease in the refractive index. Electron spin resonance experiments are carried out for the as-deposited, irradiated and annealed film. Free spin centers with concentration 1.013×1015 cm−3 are detected at g=2.0064 for the as-deposited film. These centers are assumed to be intrinsic since their density slightly decreases by laser irradiation. The defects associated with the photodarkening effect are suggested to originate from topological changes in bond length, bond angle and/or bond configuration.