Ab initio cluster calculations of hydrogenated GaAs(001) surfaces

Hydrogen adsorption on the (2x4) and (4x2) reconstructions of gallium arsenide (001) has been studied by internal reflectance infrared spectroscopy and ab initio cluster calculations with density-functional theory. The calculations are made on Ga5As4H11,13, Ga4As5H11,13, and Ga7As8H19 clusters, which model the arsenic- and gallium-dimer termination of the semiconductor surface. Excellent agreement has been achieved between the vibrational frequencies predicted by the theory and those observed in experiments. On the (2x4), hydrogen adsorbs on arsenic dimers to form isolated and coupled arsenic-monohydrogen bonds, and arsenic-dihydrogen bonds. Conversely, on the (4x2), hydrogen adsorbs on gallium dimers to form terminal and bridged gallium hydrides. The latter species occur in isolated or coupled structures involving two or three Ga atoms.