Anomalous photovoltaic effect and negative photoconductivity in thin, amorphous GaAs-Si films

An anomalous photovoltaic effect and negative photoconductivity were observed in obliquely deposited thin, amorphous GaAs, Si, and GaAs-Si films. A model of the E(r↘,k↘)-relation of amorphous semiconductors shows that some carriers in the extended states can have negative effective masses. The number of these photocarriers is high if the energetic range of the localized states is broad. This can lead to negative photoconductivity. Additionally, gradients of the densities of carriers with positive mobilities in the localized and with negative mobilities in the extended states can lead to diffusion photovoltages of several hundred volts in a single photocell with a length of 10 mm.