Theory of the Anomalous Photovoltaic Effect of ZnS

Abstract

A theory to account for anomalies observed in the photovoltage of faulted ZnS crystals is proposed. The theory assumes that the spontaneous polarization of hexagonal ZnS causes internal fields in these crystals, with opposing fields in cubic and in hexagonal material. If one then considers a unit of one cubic and one hexagonal segment, these fields will cause differences in carrier concentration, and resultant differences in photovoltage at the two band-gap barriers in such a unit. The net photovoltages of such units will be additive along the crystal. It appears that the proposed theory can account for observed photovoltages, both as to their magnitude and their reversal of sign with wavelength.