Reduction of gap states of ternary III–V semiconductor surfaces by sulfur passivation: Comparative studies of AlGaAs and InGaP

Abstract

The effects of sulfur passivation on liquid-phase-epitaxy-grown n-type InGaP and AlGaAs surfaces have been studied using x-ray photoelectron spectroscopy. The surfaces were simultaneously prepared through degreasing and the use of an aqueous (NH4)2Sx treatment in air. For InGaP, sulfur atoms initially reacted with both surface In and Ga atoms and reacted negligibly with P atoms. The band bending was reduced by 0.7 eV compared to a sputter-cleaned surface. Presumably, sulfur eliminated P-vacancy-related gap states by occupying P sites and forming In–S and Ga–S bonds. By postheat treatment at 180 °C, S atoms were not removed from the surface and band bending was reduced further by 0.1 eV. For AlGaAs, S atoms initially reacted with Ga and As, but this treatment could not remove the Al oxide previously formed in the air. Postheat treatment at 180 °C simply induced S redistribution from As to Ga and As desorption, which reduced the band bending by 0.3 eV compared to the sputter-cleaned surface—a result similar to that for GaAs.