Influence of S and Se on the Schottky-barrier height and interface chemistry of Au contacts to GaAs

The electrical properties and interface chemistry of Au Schottky-barrier contacts formed on n-type GaAs (100) surfaces that had prior exposure (at room temperature) to elemental S or Se are compared to those of Au contacts to clean surfaces (ideal contacts). The interface Fermi-level energy EiF and chemistry during contact formation were investigated by x-ray photoemission spectroscopy (XPS). The Schottky-barrier height φB was measured by current-voltage and capacitance-voltage methods on the same interfaces characterized by XPS. The exposure of clean GaAs to elemental S or Se results in formation of a ∼5 Å surface layer of Ga and As chalcogenides via a limited chemical reaction. The Schottky-barrier height for Au contacts to the S or Se exposed surfaces had a 0.2 eV variation (0.8–1.0 eV) centered about the φB=0.89 eV value for the ideal Au contact. Changes in EiF over a ∼0.4 eV range occur in response to changes in interface chemistry during surface treatment sequences that include S and Se exposure and Au deposition.