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First-principles study of native defects in CdGeAs 2

2008; American Physical Society; Volume: 78; Issue: 8 Linguagem: Inglês

10.1103/physrevb.78.085214

1550-235X

Tula R. Paudel, Walter R. L. Lambrecht,

Advanced Semiconductor Detectors and Materials

First-principles results are presented for various native defects in ${\text{CdGeAs}}_{2}$ as function of the relevant elements' chemical potentials. The defect formation energies were calculated using fully relaxed 64 atom supercells by means of the full-potential linearized muffin-tin orbital implementation of the density-functional theory in the local-density approximation (LDA). The LDA band gap is adjusted using the $\text{LDA}+U$ approach by introducing a semiempirical orbital dependent $U$ shift to the $s$ orbitals of Cd and Ge and the $d$ orbitals of Cd. The transition energies of the vacancies ${V}_{\text{Cd}}$, ${V}_{\text{Ge}}$, and ${V}_{\text{As}}$, and antisites ${\text{Ge}}_{\text{Cd}}$, ${\text{Cd}}_{\text{Ge}}$, ${\text{Ge}}_{\text{As}}$, and ${\text{As}}_{\text{Ge}}$ are calculated. Defect levels are interpreted in a simple-molecular orbital theory picture and the relation between Kohn-Sham band structures and transition levels is discussed. The vacancies are generally found to have higher energy of formation than the antisites. In particular, the somewhat deeper acceptor ${V}_{\text{Ge}}$ is found to have the highest energy of formation among the defects studied. Among the three shallow acceptors $({V}_{\text{Cd}},\text{ }{\text{Cd}}_{\text{Ge}},\text{ }{\text{Ge}}_{\text{As}})$, the lowest energy of formation is found for ${\text{Cd}}_{\text{Ge}}$, but only the ${\text{Ge}}_{\text{As}}$ antisite is expected to be active in electron paramagnetic resonance (EPR). This is consistent with experimental data, establishing a link between the EPR-active center and the shallow acceptor responsible for optical absorption. Both ${\text{Ge}}_{\text{Cd}}$ and ${\text{As}}_{\text{Ge}}$ are found to be deep donors.