The influence of sulfur on the In/GaAs(100) interface formation

The In adsorption on sulfur modified GaAs(100) surfaces was studied using high resolution soft X-ray photoemission spectroscopy (SXPS). The sulfur passivation was performed in UHV by annealing the GaAs(100) substrates in a flux of sulfur atoms. This leads to a (2 X 1) reconstructed gallium sulfide like layer at the surface. Due to the sulfur treatment the position of the Fermi level relative to the conduction band minimum (CBM) is reduced by approximately 0.46 and 0.36 eV on p- and n-type GaAs, respectively. Onto these sulfur modified surfaces indium is deposited from a Knudsen tell. From the core level emission spectra it is concluded that no alloying between gallium and indium takes place. The indium only reacts with the sulfur layer on the top, represented by a reacted component in the core level spectra, while the contribution of metallic indium clusters dominates the spectra at higher indium coverages. At approximately 4 nm indium coverage, the position of the Fermi level above the valence band maximum amounts to 1.1 and 0.8 eV for n- and p-doped samples respectively, which is higher than the Fermi level observed for the unmodified In/GaAs(100) Schottky contact (0.75 and 0.50 eV). The change in barrier height due to the sulfur passivation is attributed to a sulfur-induced interface dipole. (C) 1999 Elsevier Science B.V. All rights reserved.