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 differenct Si sites in GaAs have been examined: Si replacing a Ga atom (${\mathrm{Se}}_{\mathrm{Ga}}$ donor) and Si replacing an As atom (${\mathrm{Si}}_{\mathrm{As}}$ acceptor). We find that the stable configuration for the H-${\mathrm{Si}}_{\mathrm{Ga}}$ 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-${\mathrm{Si}}_{\mathrm{As}}$ complex is along the ${\mathrm{Si}}_{\mathrm{As}}$-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 the passivation of the impurities. The computed localized vibrational frequencies and dissocation energies of the H-Si complexes agree reasonably well with experimental results.