THEORY OF SCHOTTKY-CONTACT FORMATION ON GAAS(110)

A phenomenological theory of Schottky-contact formation to GaAs(110) surfaces at room temperature is introduced. The theory is split into two regimes: low (on the order of one monolayer) and high metal coverages. In the low-coverage regime, prior to the overlayer developing metallic characteristics, the movement of the Fermi level is proposed to occur because of universal derelaxation of the GaAs(110) surface. For these coverages, all systems are hypothesized to evolve into two types of clusters: those composed of the metal atoms themselves and those composed of disordered (amorphous) GaAs, which results from the metal atoms reacting with the GaAs surface. It is found that the GaAs surface is derelaxed underneath the clusters and that this derelaxation extends just beyond the edges of the clusters, resulting in the formation of cluster-edge-induced intrinsic surface states. For large metal depositions, the resulting barrier heights are hypothesized to be determined by the interaction of either free (not involved in compound formation with other species) metal or free As with the GaAs surface region. It is shown that, on the basis of simple considerations of the relative enthalpy of metal-arsenide formation, it is possible to decide which species is responsible for the barrier height and, thus, to account for the majority of barrier heights to the GaAs(110) surface.