SIO2 GROWTH ON GAAS BY REDUCTION OF GAAS OXIDES - SEPARATION OF STOICHIOMETRIC CHANGES FROM SIO2/GAAS BAND-LINEUP EFFECTS

The deposition of Si on oxidized GaAs(110) surfaces produces the complete reduction of the GaAs oxides and the formation of SiO2. These chemical reactions have been monitored in situ from synchrotron photoemission measurements. To discern the stoichiometry of the formed Si-oxide is a difficult task, because the Si(2p) core level shifts approximately 1.2 eV to lower kinetic energies during the chemical process. A detailed study of the system based on the comparison of the core-level binding energies and the work-function changes permits us to separate the interfacial voltage effects from the bonding charge transference and final-state relaxation contributions to the core-level shift. Thus, it can be concluded that the observed energy shift corresponds to a band-lineup variation at the SiO2/GaAs interface, and that SiO2 is formed from the beginning of the process. The band-offset variation is consistent with the decrease of an interfacial voltage related to an As excess produced in the first stage of the reduction of the GaAs oxides, and a tentative model is proposed. After the reduction of the substrate oxides, Si grows on the SiO2 layer with a modification of 0.7 eV in the Si-SiO2 chemical shift. Cluster size effects and band lineup at this interface are discussed as possible explanations.