Au-GaAs(110) interface: Photoemission studies of the effects of temperature

Abstract

Detailed photoemission studies have been performed on the Au-GaAs(110) interface at room temperature and after annealing at temperatures of up to 500?deC. The data indicate the formation of a Au-rich Au-Ga alloy in the form of medium-to-large-scale (bulklike) clusters with possible As intermixing at room temperature. The degree of intermixing increases with annealing temperature, as the clusters become thicker and more enriched in Ga. At 500?deC the As evaporates, large portions of the GaAs surface become uncovered, and evidence of a nearly pure metallic Ga phase is seen. The Fermi-level pinning behavior has also been deduced from the photoemission data. We observe pinning at a barrier height of 0.7±0.1 eV below the conduction-band minimum (CBM) for small [∼0.2 monolayer (ML)] coverages and at 0.85±0.1 eV below the CBM for coverages greater than ∼0.3 ML on n-type GaAs(110) at room temperature. We suggest that the pinning at 0.7 eV is due to an acceptor defect level and the pinning at 0.85 eV is due to a donor defect level which, due to depletion of electrons from the defect level by the Au clusters, acts effectively to pin $E_F$ on n-type GaAs. These levels are in agreement with those of the unified defect model. After heating of these films we observe a reduction in the amount of pinning due to annealing of defects and exposure of large portions of the surface. Pinning on p-type GaAs is observed at 0.5±0.1 eV above the valence-band maximum for a coverage of ∼0.2 ML at room temperature and is attributed to the same donor level. This pinning is also seen to decrease with increased annealing temperature.