Hybrid density functional studies of cadmium vacancy in CdTe

The intrinsic defect of cadmium vacancy (V_Cd) in cadmium telluride (CdTe) has been studied by first-principles calculations using potentials with both the screened hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE) approximation and the generalized gradient approximation of the Perdew-Burke-Ernzerhof form (PBE-GGA). Both results show that the T_d structure of the V_Cd defect for different charges is the most stable structure as compared with the distorted C_3v structure with one hole localized at one of the four nearest Te atoms. This indicates that the John-Teller distortion (C_3v) structure may be unstable in bulk CdTe crystal. The reason likely lies in the delocalized resonance nature of the t₂ state of the V_{m Cd} defect. Moreover, the formation energy obtained by the HSE method is about 0.6-0.8 eV larger than that obtained by the PBE method. The transition levels calculated by the PBE method and the HSE method are similar and well consistent with the experimental results.