Ga adsorption on GaAs(001) and Al-Ga-GaAs Schottky diodes grown by molecular-beam epitaxy

Ga adsorption on c(2×8) GaAs(001) prepared by molecular-beam epitaxy (MBE) has been studied. Cluster growth of the metal is observed over the whole investigated coverage range (160 {}). During photoemission the clusters are charged leading to a shift in the metal energy distribution curves. By using a simple electrostatic model, good agreement between the observed energy shifts and the size distributions observed in electron micrographs is found. The limited electrical conductivity between the metal clusters and the substrate is suggested to be due to an insulating layer of disordered GaAs. Pure Ga diodes prepared on MBE-grown GaAs(001) show high barrier heights ({~}1 eV). The high barrier can be explained by a high interface-state density localized to the disordered GaAs layer. Schottky diodes prepared by Al deposition on top of the discontinuous Ga film show barrier heights which increase with the amount of interfacial Ga. This can be explained by a model with parallel, "intermixed" diodes of Al-GaAs and Ga-GaAs.