Boron oxide interaction with silicon in silicon molecular beam epitaxy

Abstract

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 SiO2 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 Ea=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.