Effects of surface band bending on low-energy photon-induced oxidation of GaAs(110).

Abstract

Studies of photoinduced oxidation of physisorbed ${\mathrm{O}}_{2}$ on GaAs(110) at 25 K show that the surface reaction rate is strongly dependent on photon energy and substrate doping type. With 1.7-eV photon irradiation, the reaction cross section is 6.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}20}$ ${\mathrm{cm}}^{2}$ for n-type GaAs and \ensuremath{\sim}7 times higher for p-type GaAs. With 1.97-eV photon irradiation, the reaction cross section is 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ for n-type GaAs and \ensuremath{\sim}8 times higher for p-type GaAs. We show that the energy distribution of the photoexcited electrons in the conduction band relative to the ${\mathrm{O}}_{2}$ electron-affinity level is the critical parameter in determining reaction with the substrate. Differences in the reaction rate reflect the energy dependence of the resonance coupling of excited substrate electrons to physisorbed ${\mathrm{O}}_{2}$. Surface band bending and the photon excitation energy control the matching of these electrons with the ${\mathrm{O}}_{2}$ electron-affinity level.