Self-compensation in chlorine-doped CdTe

Defect energetics, charge transition levels, and electronic band structures of several Cl-related complexes in CdTe are studied using density-functional theory calculations. We investigate substitutional chlorine (Cl(Te) and Cl(Cd)) and complexes formed by Cl(Te) with the cadmium vacancy (Cl(Te)-V(Cd) and 2Cl(Te)-V(Cd)) and the Te(Cd) antisite (Cl(Te)-Te(Cd)). Our calculations show that none of the complexes studied induce deep levels in the CdTe band gap. Moreover, we find that Cl(Te)-V(Cd) and Cl(Te) are the most stable Cl-related centers in n-type and p-type CdTe, under Te-rich growth conditions, showing shallow donor and acceptor properties, respectively. This result suggests that the experimentally-observed Fermi level pinning near midgap would be originated in self-compensation. We also find that the formation of the Cl(Te)-Te(Cd) complex passivates the deep level associated to the Te antisite in neutral charge state.