Unpinned Schottky barrier formation at metal–GaAs interfaces

Abstract

We have used soft x-ray photoemission spectroscopy measurements to demonstrate that metal–GaAs interfaces can exhibit relatively unpinned Fermi level (Ef) movements. For clean GaAs (100) surfaces obtained by molecular-beam epitaxy (MBE) growth and thermal decapping of a protective As overlayer, the metals Au, Al, Cu, and In produce a 0.6–0.7-eV range of Ef stabilization. For a given metal, this stabilization occurs at the same energies for n-type and p-type GaAs. Furthermore, Ef movements are metal-dependent and can evolve over multimonolayer coverages. These results are examined with respect to pronounced differences in semiconductor quality between MBE versus melt-grown GaAs and in the context of previous GaAs Ef measurements. A self-consistent analysis of the junction electrostatics accounts for the functional dependence of barrier height on metal work function. The results highlight the importance of bulk quality as well as interface specific phenomena in controlling the Schottky barrier formation at metal/III–V compound semiconductor interfaces.