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

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 (OTe-TeCd) complex. This complex is energetically favored over both isovalent (OTe) and interstitial oxygen (Oi), in the Te-rich limit. We find that the incorporation of oxygen passivates the harmful deep energy levels associated with (TeCd), suggesting an improvement in the efficiency of CdTe based solar cells. Substitutional (OCd) 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.