B2O3 decomposition by reaction with Si has been studied in situ by Auger electron spectroscopy in a Si molecular beam epitaxy environment as a function of the silicon flux (0<JSi<14.5 Å/min) and the growth temperature (25°C<Ts<800°C) . Quantitative analysis of Auger signals indicates that oxygen is associated with both SiO2 and B2O3. Below a critical substrate temperature (Ts<500°C), no reaction occurs between B2O3 and Si. When the substrate temperature is higher than 500°C, the atomic fraction of Si and B increases while that for SiO 2 and B2O3 decreases. The chemical reaction which causes the signal changes is thermally activated, as shown by the dependence of the oxygen on boron concentration ratio, I[O/B], which drops rapidly according to an Arrhenius relation with an activation energy E a=4.5±1.0 eV. From the experimental results, we propose a model which involves B2O3 reduction by Si to form the (Si-B) and SiO2 phases. SiO2 is then decomposed by Si bombardment on the surface to produce SiO which subsequently desorbs.
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