H PASSIVATION OF SI IMPURITIES IN GAAS

The equilibrium sites, vibrational frequencies, and electronic properties of interstitial H in GaAs doped with Si have been studied by first-principles calculations in the local density approximation within a supercell approach. Two different Si sites in GaAs have been examined: Si replacing a Ga atom (Si(Ga) donor) and Si replacing an As atom (Si(As) acceptor). We find that the stable configuration for the H-Si(Ga) complex is the antibonding-Si site. The lattice undergoes a large relaxation and the Si-As bond is almost broken. The stable site for the H-Si(As) complex is along the Si(As)-Ga bond. H binds to the Si and Ga atoms forming a three-center bond. In both cases the lattice relaxation is essential in order to obtain the passivation of the impurities. The computed localized vibrational frequencies and dissociation energies of the H-Si complexes agree reasonably well with experimental results.