Staelber-Wronski effect in hydrogenated amorphous germanium films

The authors report on the optoelectronic properties of high-quality a-Ge:H films prepared by the RF sputtering method and on their photodegradation resulting from light soaking at different temperatures and under different irradiation conditions (Staebler-Wronski effect). The material parameters of interest for solar device manufacturing presented are among the best reported to date: a low density of electron states in the pseudogap, a temperature-activated dark conductivity (E_a⩾0.5 eV) down to below 200 K, and a photo-to-dark conductivity ratio of up to 2.0 under AM1 conditions. The dark conductivity and the photoconductivity of the a-Ge:H samples decrease after light soaking. The changes are metastable and both the defect formation and the defect annealing processes are temperature activated. As in the case of a-Si:H films, the time evolution of the conductivity changes is well represented by a stretched exponential type of decay with activated time constants