ON THE ORIGIN OF THE ANOMALOUS PHOTOVOLTAIC EFFECT IN ZINC SULFIDE

It was shown that earlier models failed to account for all the features of the APE. The only objection to Hutsons model was that it was incomplete. By extending Hutsons model and for mulating the problem in terms of independent photovoltage generators in each segment of the crystal, one can account for all the features of the spectral response of the APE. The expression derived for the dependence of the photovoltage on an external applied stress, together with the results of the stress experiments on mixed crystals, verifies the assumption of the origin of the photovoltage, viz., that the photovoltages arise from piezoelectric fields set up by permanent internal strains formed during the growth process. The experiment on single crystal hexagonal ZnS not only added strength to the proposed origin of the APE, but also successfully tied together the information on direction of crystal growth, pyroelectric effect, and the positive peak polarity. This experiment also verified the calculation of the photovoltage generated in a non-uniformly strained piezoelectric crystal.