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.