The anomalous photovoltaic effect in zinc selenide

An anomalous photovoltaic effect has been observed in hollow, needle-shaped crystals of zinc selenide. Photovoltages up to 100 V have been measured in samples which exhibit coloured bands of uniform birefringence and dark striations under crossed polarizers in the polarizing microscope. Two reversals of the sign of the photovoltage occur when the wavelength of the exciting light is reduced from 5000 to 4000 AA. The effect is very similar to the anomalous photovoltaic effect in zinc sulphide, which was first reported by Ellis et al (1958). A qualitative explanation of the effect is offered in terms of the asymmetry of heterojunctions along the polar axis of a needle crystal.