Nature and energy structure of impurity and intrinsic defects in V-doped Cd1−xHgxTe

Abstract

The nature and the energy structure of impurity and intrinsic defects, including the formation of anisotropic impurity centres, are determined in V-doped semi-insulating Cd1−xHgxTe (x ⩽ 0.037) crystals which were grown by the Bridgman technique for the first time. From detailed analysis of the spectral dependence of the photodiffusion current data obtained for the different directions of light propagation in crystals as well as the impurity absorption spectra, we established that for the investigated crystals anisotropic V2+ and V3+ centres are formed. Two mechanisms of the electron photogeneration from the ground impurity state to the conduction band (direct photoionization and auto-ionization from the excited state V2+ ions) are established. It is shown that the efficacy of the auto-ionization of electrons depends on the position of the excited state relative to the conduction band bottom. The photoinduced impurity centres are formed as a result of the illumination of the crystals with the light with energy about 1.50 eV. The nature and photoionization energy of these photoinduced centres are determined. The scheme of the impurity and intrinsic defects energy levels in the energy gap of the investigated crystals is presented.