Tailoring of defect levels by deformations: Te-antisite in CdTe

Abstract

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.

Small hole polaron in CdTe: Cd-vacancy revisited

“…Nonmagnetic HSE06 calculations of the with T d geometry still give a metallic solution (not shown). In our previous paper 24 we showed that HSE06 calculations lowered the valence band edge by 0.26 eV. In addition, the defect state has now moved deeper into the band gap.…”

“…For geometry optimizations, the atoms were relaxed until the Feynman-Hellman forces on each atom reached 0.01 eV/Å. For the k-point sampling we used a Monkhorst-Pack (for LDA) and Gamma-centered (for HSE06) (2 × 2 × 2) grid with a Gaussian smearing of 0.025 eV, which was earlier shown to reproduce converged features of the CdTe valence band 24 . As discussed earlier 24 , the (2 × 2 × 2) k-point grid is not sufficient to obtain a smooth conduction band edge but fortunately both the Cd vacancy and Te antisite defect states originate from the valence band and we concluded that the insufficient resolution of the conduction band edge is negligible in the context of the here presented results.…”

Characterization of point defects in CdTe by positron annihilation spectroscopy

“…2(a)) almost into the plane of lower Te atoms. 4 A split interstitial configuration is predicted for the À2 charge state, the antisite Te atom displaces on to the Te-1 to Te-2 line, and the Te-2 atom is displaced away from Te-1 along the same line. 1 The positron wavefunction exhibited localization, and the resulting positron lifetimes for the two charge states were found to be similar (Table I); these were again approximately 10 ps smaller than the lifetime for the unrelaxed V Cd defect.…”

“…27,30 Recent firstprinciples calculations of point defects in CdTe have provided further insight on local structure and stability. [1][2][3][4][5]31 Possible relaxed geometries of the two stable charge states, À1 and À2, of the Cd vacancy, 1,3 and for the À1 charge state of Cl-donor A-center, V Cd with a Cl Te nearest neighbor, 2 have been reported. The other point defect considered of particular importance in these materials is the Te antisite; this has also been studied and relaxed structures for the three charge states, Te þ2…”

First-principlesDFT+GWstudy of oxygen-doped CdTe

“…Tellurium antisite (Te Cd ) has been proposed as a possible candidate to form a deep donor level, which is believed to be responsible for the pinning of the Fermi energy near the middle of the band gap in semi-insulating CdTe [16,[67][68][69]. The ground-state structure of (Te Cd ) in the neutral charge state undergoes a Jahn-Teller distortion [69,70]. In T d symmetry, electrons are localized at the high-symmetry anion site, leaving the localized electron manifold in a degenerate state.…”