] CdGeAs2: Point Defects

First-principles results were presented for various native defects in CdGeAs2 as a function of the relevant element’s chemical potential. The defect formation energies were calculated using fully relaxed 64-atom super-cells by means of the full-potential linearized muffin-tin orbital implementation of the density-functional theory in the local-density approximation. The local-density approximation band-gap was adjusted using the LDA+U approach by introducing a semi-empirical orbital dependent U shift to the s orbitals of Cd and Ge and the d orbitals of Cd. The transition energies of the vacancies VCd, VGe, and VAs, and antisites GeCd, CdGe, GeAs, and AsGe were calculated. Defect levels were interpreted in a simple-molecular orbital theory picture and the relationship between Kohn-Sham band structures and transition levels was considered. The vacancies were generally found to have a higher energy of formation than did the antisites. In particular, the somewhat deeper acceptor VGe was found to have the highest energy of formation among the defects studied. Among the three shallow acceptors (VCd, CdGe, GeAs), the lowest energy of formation was found for CdGe, but only the GeAs antisite was expected to be active in electron paramagnetic resonance. This was consistent with experimental data, establishing a link between the EPR-active center and the shallow acceptor responsible for optical absorption. Both GeCd and AsGe were found to be deep donors.

First-Principles Study of Native Defects in CdGeAs2. T.R.Paudel, W.R.L.Lambrecht: Physical Review B, 2008, 78[8], 085214 (11pp)