Energetics and hydrogen passivation of carbon-related defects in InAs and In0.5Ga0.5As

We perform ab initio pseudopotential calculations for studying the stability of carbon-related defects and the atomic model for the hydrogen passivation of substitutional carbons in InAs. Among various C-related defects, the most stable one is found to be a substitutional C acceptor occupying an As site. As compared to GaAs, substitutional C impurities are found to have higher formation energies, due to large lattice distortions surrounding the C atom, thus, C incorporation into bulk InAs is more difficult. Because of the small atomic radius and deep atomic energy levels of C, when C occupies an In site, its defect energy level lies below the valence band maximum (VBM), and it behaves as an acceptor, however, the formation energy is much higher than for C-As. We note that an inversion between the VBM and the C-In energy level takes place as pressure increases. For both the substitutional C-As and C-In, we find that hydrogen neutralizes the electrical activity of accepters by occupying a bond-centered site between the C atom and one of its neighbors. In an In0.5Ga0.5As alloy, the C acceptor is found to favor an As site with In neighbors, with the formation energy lying between InAs and GaAs. Thus, the calculated acceptor concentration of 10(17) - 10(18) cm(-3) is much lower than the maximum carrier density achievable in GaAs.