Boron oxide interaction with silicon in silicon molecular beam epitaxy

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<J_Si<14.5 Å/min) and the growth temperature (25°C<T_s<800°C) . Quantitative analysis of Auger signals indicates that oxygen is associated with both SiO₂ and B₂O₃. Below a critical substrate temperature (T_s<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.