Electrical and optical characteristics of deep levels in vanadium-doped Cd0.96Zn0.04Te materials by photoinduced current, capacitance, and photocapacitance transient spectroscopies

Abstract

A complete quantitative analysis of electrical and optical properties is carried out on the vanadium transition metal in semi-insulating and n type conductor Cd0.96Zn0.04Te crystals using deep level transient spectroscopy, deep level optical spectroscopy, and photoinduced current transient spectroscopy. Four deep levels are mainly detected, with activation energies at Ec−0.95 eV, Ec−0.78 eV, Ev+0.68 eV, and Ev+0.2 eV. Their electrical and optical characteristics (thermal and optical cross sections, concentrations, and apparent activation energies) are determined. The 0.68 eV hole level and the 0.95 eV electron trap are related to the vanadium doping. These two levels are proposed to be originated from the same defect that interacts with the valence and conduction band, respectively. We have demonstrated that the 0.95 and 0.78 eV electron traps present capture barrier energies with values of 0.2 and 0.15 eV, respectively. The observed resonance bands on the optical cross sections σno and σpo of the 0.95 eV level are attributed to d→d* internal transitions of the V2+(3d3) and V3+(3d2) ions on Cd sites, respectively. Based on the above result, the 0.95 eV level is formally identified to the V2+/V3+ single donor and its real thermal ionization energy locates it near the midgap at 0.75 eV below the conduction band. This level is shown to be the donor trap that explain the semi-insulating character of the V doped CdZnTe materials. It is shown also that the 0.78 and 0.95 eV play a key role in the photorefractive properties of the V doped CdZnTe crystals.