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 and Cl) and complexes formed by Cl with the cadmium vacancy (Cl-V and 2Cl-V) and the Te antisite (Cl-Te). Our calculations show that none of the complexes studied induce deep levels in the CdTe band gap. Moreover, we find that Cl-V and Cl 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 complex passivates the deep level associated to the Te antisite in neutral charge state.