It has been proposed that a harpooning-like silicon-to-O2 electron-transfer process to form an O2 - like precursor is the crucial first step in the oxidation of Si(111). Here we use 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 O2 - 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 O2 - like precursor is involved in the photoenhancement of the oxidation process. © 1991 The American Physical Society.