Surface photovoltage measurements on pyrite (100) cleavage planes: Evidence for electronic bulk defects

Abstract

Temperature dependent contactless surface photovoltage measurements by photoelectron spectroscopy have been performed on cleaved (100) surfaces of pyrite (FeS2) single crystals. The results have been fitted by thermionic emission, recombination, and tunneling models for the majority carrier transport to the surface. Neither of them is able to explain the small photovoltages consistently. By calculating electronic defect levels due to the sulfur deficiency of pyrite a high number of defect states in the band gap is obtained. As a consequence a nonuniform depletion layer is expected with a part of the band bending potential falling off at a very small distance near the surface. The small photovoltages can be explained by a tunneling of majority carriers through the narrow barrier and by recombination losses due to the defects.