Schottky barriers on anodic-sulfide-passivated GaAs and their stability

The effects of anodic (NH₄)₂S passivation of n-GaAs Schottky diodes have been investigated. When these Schottky diodes are prepared on anodically treated n-GaAs in (NH₄)₂S solution, the Schottky barrier height is lowered by at least 200 meV, and the interface trap density is estimated to be 5.5×10¹² cm^-2 which is two orders less than that of the untreated sample. It is observed that the Schottky barrier height or the position of the Fermi level at the surface is not stable for samples treated with a small current density (∼83 μA/cm ²), but is significantly stable for samples treated with a large current density (∼1 mA/cm²). The stability of passivation is sensitive to the photon energy of the excitation source. Although for a longer-wavelength (λ=514 nm) illumination the passivation is stable, for a shorter-wavelength (λ=325 nm) illumination, the passivation is unstable. The photoluminescence intensity is found to rapidly decay due to photon-assisted oxidation. As compared to the (NH₄)₂S dip treatment, the anodic (NH₄)₂S treatment improves the stability of passivation.