Influence of cation vacancies and Bi impurity on the electronic structure and photoelectric properties of orthorhombic GeS

Quantum-chemical studies of GeS electronic structure containing intrinsic point defects (vacancies in the cation (VGe) and anion (VS) sublattices), isolated substitutional impurities BiGe and {VGe–BiGe}-type complexes were performed using density functional theory in the LDA+U-approximation as well as their role in the formation of photoelectric characteristics of the crystals was discussed. It was established that the localization of Bi impurity predominantly in the germanium positions induces the appearance of donor-type levels in the bandgap compensating the acceptor levels formed by cation vacancies which lead to the increase of dark resistivity as well as the sharp increase of photosen…