Ab initio study of defects in compound semiconductors

Abstract

We investigate the stability of carbon acceptors and defect complexes composed of carbon and hydrogen in GaAs through first-principles pseudopotential calculations. A carbon-hydrogen $C^{-}_As-(HC_As)^0$ complex with two $C_As$ atoms at second neighbor As sites is found to be energetically more favorable than the isolated configuration of $C^{-}_As$ and $H-C_As$. We also find that a $(H-C_As)_2$ complex containing two H atoms is more stable than two isolated $H-C_As$ pairs. Hydrogen dissociation from the $C_As^{-}-(HC_As)^0$ center upon annealing leads to the formation of a $C_As-C_As$ pair, and the $C_As-C_As$ complex subsequently dissociates into two isolated $C_As$ acceptors. Here we propose a dissociation process that involves a C-C split interstitial complex at an As site and a second neighbor As vacancy, with an energy barrier of about 1.7 eV which is similar to that for Zn diffusion. We investigate the atomic geometry and energetics of Cl-related defects in ZnTe through first-principles pseudopotential calculations. We find a new type of defect which results from large lattice relaxations, with $C_3v$ symmetry and triple broken bonds around the Cl impurity at a Zn sublattice site. The triple-broken-bond structure of $Cl_Zn$ behaves as an acceptor and this defect is more stable than the DX-like broken-bond state of $Cl_Te$. Thus, we suggest that the triple-broken-bond centers are very effective in donor compensation, particularly, in heavily Cl-doped ZnTe as well as in samples grown under Te-rich conditions. We calculate the defect formation energies and concentrations of native and Mg-related defects in wurtzite and zincblende GaN using a first-principles pseudopotential method. For both the wurtzite and zincblende structures, vacancies are found to be more stable than other intrinsic defects, such as interstitials and antisites. Under Ga-rich condition, the concentration of $V^+_N$ is estimated to be about $10^17cm^{-3}$ in the absence of other impuriti...