Thermal and photochemical oxidation of Si(111): Doping effect and the reaction mechanism

It has been proposed that a ‘‘harpooning’’-like silicon-to-${\mathrm{O}}_2$ electron-transfer process to form an ${\mathrm{O}}_2^{\mathrm{-}}$-like precursor is the crucial first step in the oxidation of Si(111). Here we use δ doping of silicon with boron to reduce the electron population of the silicon-surface adatom dangling bonds. We find that indeed the extent of oxidation and the amount of the ${\mathrm{O}}_2^{\mathrm{-}}$-like species on the surface are greatly reduced by the doping. Moreover, we find an analogous suppression of the photo-oxidation process. The latter result indicates that the photodissociation of the same ${\mathrm{O}}_2^{\mathrm{-}}$-like precursor is involved in the photoenhancement of the oxidation process.