Anomalous photovoltaic effect in vacuum-deposited CdTe films

CdTe films of thicknesses varying from 125 to 1250 nm were vapour deposited onto glass substrates at oblique incidence in vacuum at substrate temperatures varying from room temperature to 250 °C. The samples are irradiated with an He-Ne laser from the direction of the deposited layer and through the substrate. It was found that the film thickness and substrate temperature play an important role in changing the magnitude and polarity of the photovoltages generated in CdTe films. A reversal in the polarity of the photovoltage is obtained in certain films depending on the deposition parameters. An attempt is made to interpret the results.