(An) ab initio study on the physical properties of defects in semiconductors

Abstract

Various physical properties of defects in semiconductors such as GaAs, InP, and ZnSe are studied through the first-principles pseudopotential calculation. For GaAs and InP, the structural stability and its pressure behavior of donor-induced defect states are examined. The atomic structure and the local vibrational mode of defects are also presented. The stability of donor impuritues are interpreted by the chemical bonding effects, which are associated with broken-bond and breathing-mode latice relaxations. The calculated shallow-to-deep level transitions at high pressure are in good agreement with experimental results. The compensation mechanism of acceptors in heavily doped GaAs and ZnSe is investigated. Calculating the formation energies of various defects, the defect and free hole concentrations are determined as a function of dopant concentration and stoichiometric condition. For a carbon (C) dopant in GaAs, the substitutional $C_{As}$ is found to be most stable, showing that C acts as an acceptor. The hole compensation and the diffusion mechanism of the C atom in the high doping regime are examined. The calculated maximum hole concentration is estimated to be about $10^{20}cm^{-3}$, in good agreement with experimental results. However, above this concentration, the acceptors are compensated by the [100]-split interstitial $(CC)_{[100]}$ complexes, which act as a donor. A new mechanism for the C diffusion process is proposed, accompanied with the formation and dissociation of the $(CC)_{[100]}$ complex, with the activation energy lower than that for atomistic diffusion. This result successfully explain the hole compensation and the diffusivity observed for heavily C-doped GaAs. For ZnSe doped with N impurities, the compensation mechanism of N acceptors is presented. The substitutional $N_{Se}$ acceptor is found to be more stable than other native defects and N-related defects. However, as N concentration increases above $10^{18}cm^{-3}$, the concentration o...