The characteristics of electronic states of Cd-vacancies in CdTe, an important semiconductor for various technological applications, are under debate both from theoretical and experimental points of view. Experimentally, the Cd-vacancy in its negative charge state is found to have C3v symmetry and a (−1/−2) transition level at 0.4 eV. Our first principles density functional calculations with hybrid functionals confirm for the first time these experimental findings. Additionally, we find that the C3v symmetry and the position of the (−1/−2) transition level are caused by the formation of a hole polaron localised at an anionic site around the vacancy.

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The properties of the Te-antisite defect in the neutral state in CdTe were examined using ab initio calculations. The influence of three types of deformations (1D, 2D and 3D) on the defect energy levels and formation energies was investigated. It was found that the 2D deformation is the most effective for pushing the defect levels towards the band edges and opening up the bandgap of the semiconductor, and hence may improve the performance of CdTe as a detector material. We studied the defect levels and their occupancies including Jahn-Teller distortions. The Jahn-Teller distorted configuration places the 2A1(a) defect level closer to the valence band and this defect level position coincides with the 'unknown deep donor' measured in some experiments. Partial densities of states and band structures have been analysed to understand the arrangement of the defect bonds.