Phenomenological model of anomalously high photovoltages generated in obliquely deposited semiconductor films

Photovoltage in obliquely deposited films of semiconductors is found to be much higher in magnitude than the corresponding band gap of the semiconductor. Also, the magnitude of the photovoltage depends on the angle of deposition, the separation between the electrodes, the wavelength of the incident light, the intensity of the illumination and temperature, but this behavior is not understood well. In this work a phenomenological model of the generation of photovoltage along the horizontal plane of the obliquely deposited films on transparent substrates is presented for the first time. The model is based on the presence of obliquely grown grains separated by parallel grain boundaries and the existence of grain boundary potential barriers across the grain boundaries. In the case of semiconductor films with a high absorption coefficient for short wavelengths in the visible range, there occurs a relatively large photogeneration of carriers on the front side of the grain boundaries rather than on the back side,...