First-principles calculations of molecular- and atomic-hydrogen reactions on As-terminated GaAs(100) surfaces

We have investigated the reaction of molecular and atomic hydrogen on an As-terminated GaAs(100) surface, on which As dimers exist, by performing a first-principles total-energy calculation. According to the present calculations, the ${\mathrm{H}}_2$ molecule neither dissociates nor sits on the surface while the H atoms sit on several sites accompanied by As-dimer distortion. The As-dimer distortion is well described by the simple electron counting model, taking orbital energies into consideration. We have also found that the total energy of the H-atom-adsorbed surface is comparable to that of the GaAs(100) 2×4 surface exposed to arsine and hydrogen gases.