SiO2growth on GaAs by reduction of GaAs oxides: Separation of stoichiometric changes fromSiO2/GaAs band-lineup effects

Abstract

The deposition of Si on oxidized GaAs(110) surfaces produces the complete reduction of the GaAs oxides and the formation of ${\mathrm{SiO}}_2$. 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 ∼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 ${\mathrm{SiO}}_2$/GaAs interface, and that ${\mathrm{SiO}}_2$ 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 ${\mathrm{SiO}}_2$ layer with a modification of 0.7 eV in the Si-${\mathrm{SiO}}_2$ chemical shift. Cluster size effects and band lineup at this interface are discussed as possible explanations.