Effects of Growth Atmosphere on Photovoltaic Properties of ZnS Crystals

Publisher Website
Google Scholar
Abstract
ZnS crystals were grown by sublimation in the presence of either H2S (``group S'') or a mixture of Ar and HCl (``group Cl''). Electroabsorption and polar rectification measurements indicate that permanent, high internal electrical fields exist in crystals of both groups. The anomalous photovoltaic effect (APE) is, however, observed only in the crystals of group S. For both groups, the sign of carriers excited by ir illumination was established by point-contact rectification. The Fermi level in the dark, in group S crystals, was found to be within 0.9 eV of the valence band, while in group Cl it lies in the upper half of the forbidden gap. These measurements, along with photoluminescence results indicate that the free-electron lifetime is considerably longer in group Cl crystals than in group S crystals. This difference in lifetime furnishes a simple explanation for the absence of the APE in crystals of group Cl.