First-principlesDFT+GWstudy 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.

Self-compensation in phosphorus-doped CdTe

“…The formation energy of a given defect or impurity determines its concentration. 34 The defect formation energy in charge state q and arbitrary ionic configuration can be expressed as 6,[35][36][37]…”

“…It should be noted that all of these defects are in ground-state con-figurations, i.e. all the valence bands are full and all the conduction bands are empty; thus, the self-interaction and band gap error on the formation energy is expected to be small at DFT level, only a correction in the absolute position of the VBM is required (∆E VBM = −0.74 eV in the case of CdTe) 6,36 to consider it as a proper reference for the Fermi level. Under Te-rich growth conditions, for values of E F higher than VBM + 0.56 eV (point A in Figure 3), we find that the most stable configuration is the substitutional acceptor (P Te ) −1 .…”

First-principles DFT +GW study of the Te antisite in CdTe

“…This approach is justified because we consider finite-size effects at the DFT level. Moreover, quasiparticle corrections are largely invariant with respect to the supercell size 43,55,56 and, at the high-symmetry points their differences are up to 0.1 eV. The relaxation energies were calculated using 512-atom supercells.…”

“…In order to investigate these large discrepancies among theoretical calculations, in the present work we investigate the formation energies, charge transition levels and quasiparticle defect states of (Te Cd ) in CdTe using the state-of-the-art DFT + GW formalism [40][41][42][43] , which is free of the well-known band gap error of DFT. According to our results, (Te Cd ) induces a deep level at VBM + 0.99 eV, exhibiting a negative-U effect.…”

Defect properties of Sn- and Ge-doped ZnTe: suitability for intermediate-band solar cells

“…In this work, we investigate the role of Sn and Ge as impurities in ZnTe. We calculate their formation energies and charge transition levels within the DFT + GW method, [42][43][44][45] which combines quasiparticle energies obtained within the GW approximation with total energy calculations based on the density functional theory (DFT). We find that under Zn-rich growth conditions the compensation mechanisms in Sn-and Ge-doped ZnTe are favorable for the formation of an isolated and halffilled intermediate-band, greatly enhancing the solar energy conversion efficiency by enabling the absorption of sub-bandgap photons in a two-step excitation process.…”