Development of anomalously high photovoltages in obliquely deposited semiconductor films

Anomalously large Photovoltages (V_och) is observed between two horizontal electrodes, separated by a distance of _~ 1 cm, placed on the obliquely deposited semiconductor thin films on transparent substrates. This photovoltage depends on the angle of deposition beta from the normal and in certain films has been found to be maximum for the angle of deposition beta _~ 45deg. A number of investigations have found V_och to be much higher in magnitude than the corresponding band gap of the semiconductor. The magnitude also increased linearly with the separation L between the electrodes and intensity of illumination Pin. In this work we have given a phenomenological model of the generation of photovolatge along the horizontal plane of the obliquely deposited films. 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. The characteristics such as the dependence of Voch on the wavelength lambda of the incident monochromatic light, the resistivity p of the film, angle of deposition beta and the temperature T of measurement can be understood well with the help of this model.