We have studied the stability of neutral and charged Ge substitutional defects (donor, acceptor and molecular) in bulk GaAs host. To correct the severe underestimation given by the local density approximation (LDA) in predicting bandgaps, we have applied the LDA + U scheme (Dudarev et al 1998 Phys. Rev. B 57 1505) to the gallium d orbitals. We have aligned the LDA calculated band edges of GaAs to those calculated at LDA + U level. Then, we have corrected the thermal ionization energies (LDA derived) for the defects considered. The effect of atomic distance in the self-compensation mechanism in the case of Ge2 donor–acceptor defective cells was evaluated. Our results are compared with previous results on IV-doped III–V alloys. We found that self-passivation is the main mechanism for the thermodynamic stabilization of both defective cells and alloys. We have established a relationship between the energy of stabilization versus (1) the amount of molecular Ge2 in the alloys and (2) the distance between Ge donor–acceptor atoms in the supercells, finding an almost linear relationship. We conclude that Ge2-doped GaAs defective systems behave as extremely diluted (GaAs)1−xGe2x alloys (x → 0).
Amphoteric behavior of Ge in GaAs: An LDA analysis
GIORGI, Giacomo;
2011
Abstract
We have studied the stability of neutral and charged Ge substitutional defects (donor, acceptor and molecular) in bulk GaAs host. To correct the severe underestimation given by the local density approximation (LDA) in predicting bandgaps, we have applied the LDA + U scheme (Dudarev et al 1998 Phys. Rev. B 57 1505) to the gallium d orbitals. We have aligned the LDA calculated band edges of GaAs to those calculated at LDA + U level. Then, we have corrected the thermal ionization energies (LDA derived) for the defects considered. The effect of atomic distance in the self-compensation mechanism in the case of Ge2 donor–acceptor defective cells was evaluated. Our results are compared with previous results on IV-doped III–V alloys. We found that self-passivation is the main mechanism for the thermodynamic stabilization of both defective cells and alloys. We have established a relationship between the energy of stabilization versus (1) the amount of molecular Ge2 in the alloys and (2) the distance between Ge donor–acceptor atoms in the supercells, finding an almost linear relationship. We conclude that Ge2-doped GaAs defective systems behave as extremely diluted (GaAs)1−xGe2x alloys (x → 0).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
