Modification of the photoelectric properties of undoped hydrogenated amorphous silicon films under preliminary illumination at elevated temperatures

The effect of preliminary weak illumination at elevated temperatures on the photoelectric properties of undoped $\alpha$-Si:H films is investigated. It is found that the dark conductivity and photoconductivity of films increases with the preliminary-illumination intensity, and the parameter $\gamma$ determining the dependence of the photoconductivity on the illumination intensity decreases due to an increasing fraction of the bimolecular recombination of electrons at energy levels of the tail of the density of states of the conduction band. It is assumed that this effect may be induced by the presence of an uncontrolled oxygen impurity and an increase in the concentration of electrically active oxygen as a result of preliminary illumination of the films at elevated temperatures.