First-principles DFT plus GW study of oxygen-doped CdTe

Abstract

The role of oxygen doping in CdTe is addressed by first-principles calculations. Formation energies, charge transition levels, and quasiparticle defect states are calculated within the DFT + GW formalism. The formation of a new defect is identified, the (O-Te-Te-Cd) complex. This complex is energetically favored over both isovalent (O-Te) and interstitial oxygen (O-i), in the Te-rich limit. We find that the incorporation of oxygen passivates the harmful deep energy levels associated with (Te-Cd), suggesting an improvement in the efficiency of CdTe based solar cells. Substitutional (O-Cd) is only stable in the neutral charge state and undergoes a Jahn-Teller distortion. We also investigate the diffusion profiles of interstitial oxygen and find a low-energy diffusion barrier of only 0.14 eV between two structurally distinct interstitial sites.