Effect of excited-oxygen exposures on spectra and transition density of states for cleaved Si(111) from L1L2,3V and L2,3VV Auger transitions

Abstract

Detailed AES measurements for clean cleaved and excited-oxygen exposed silicon surfaces, at room temperature, are reported. For oxygen exposures in the range 10^-7to 10^-4Torr s a continuous shift, to a maximum of 2.2 eV was observed in the negative excursion of both the L₁L_2,3V and L_2,3VV (N'(E)) Auger peaks. Higher oxygen doses, up to 10^-1Torr s, did not alter the 2.2 eV shift. For exposures >or=10^-5Torr s the formation of SiO₂was detected. The derived transition density of states curves showed (i) that the 'dangling bond' surface states associated with the clean surface were removed for oxygen exposures >or=10^-7Torr s and (ii) that a number of oxygen induced peaks appeared at well defined energies below the vacuum level. For the range of exposures studied, the valence band spectroscopic data reported have been interpreted as showing the simultaneous existence of both atomic and molecular chemisorption states and their coexistence with SiO₂formation during the early oxidation stage.