Abstract
The coexistence in Te-rich CdTe of substitutional Cl-dopants, ClTe, which act as donors, and Cd vacancies, VCd−1, which act as electron traps, was studied from first principles utilising the HSE06 hybrid functional. We find ClTe to preferably bind to VCd−1 and to form an acceptor complex, (ClTe–VCd)−1. The complex has a (0,-1) charge transfer level close to the valence band and shows no trap state (deep level) in the band gap. During the complex formation, the defect state of VCd−1 is annihilated and leaves the Cl-doped CdTe bandgap without any trap states (self-purification). We calculate Cl-doped CdTe to be semi-insulating with a Fermi energy close to midgap. We calculate the formation energy of the complex to be sufficiently low to allow for spontanous defect formation upon Cl-doping (self-compensation). In addition, we quantitatively analyse the geometries, DOS, binding energies and formation energies of the (ClTe–VCd) complexes.
Highlights
The coexistence in Te-rich CdTe of substitutional Cl-dopants, ClT e, which act as donors, and Cd vacancies, VC−d1, which act as electron traps, was studied from first principles utilising the HSE06 hybrid functional
The A-center formation is explained by the formation of a defect complex consisting of ClT e and VC−d2.12 The generally accepted model gives chlorine a similar role as lithium has in Si compensation in the presence of residual acceptors
Our calculations reveal the following: a) the donated electrons of Cl are directly participating in the complex formation: Te-rich p-type CdTe is dominated by creating a VC−d2 with which ClT+1e forms the complex
Summary
Our calculations were performed using the VASP (Vienna Ab-initio Simulation Package) code[23] employing the screened hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06)[24,25] with a screening parameter of 0.2 Å−1 and a mixing parameter of 0.25. In the number of atoms for the i-th atomic species between the defect-containing and defect-free supercells. Q is the defect charge, EV BM is the valence band maximum of bulk CdTe. EF is the Fermi level which varies in the energy range between EV BM and conduction band minimum (EC BM). Total energy calculations of charged defects in finite-size supercells include unwanted defect-defect interactions.[27,28] Many of the known correction schemes are either computationally too expensive for HSE06 calculations or not generally reliable to minimize the errors.[27,28] On the other hand, a computationally cheap and reliable correction scheme is “potential alignment”,29,30 where the potential in the defect cell is aligned to that of bulk by δV BM.
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