Boron doping concentrations ≳6×1019 cm-3 were found to increase Si(001) growth rates RSi at low temperatures while decreasing RSi at higher temperatures during gas-source molecular beam epitaxy (GS-MBE) from Si2H6 and B2H6. In order to probe the mechanisms governing these effects, Si(001) samples with B coverages θB ranging from <0.05 to ≃0.5 ML were prepared by exposing clean Si(001)2×1 wafers to B2H6 doses between 2×1017 and 4×1020 cm-20 at 200-400°C. The samples were then heated to 700°C to desorb the hydrogen, cooled to 200°C, and exposed to atomic deuterium until saturation coverage. D2 temperature programmed desorption spectra exhibit β2 and β1 peaks due to dideuteride and monodeuteride desorption at 405 and 515°C as well as new B-induced peaks, β*2 and β*1, at 330 and 470°C. Increasing θB increases the area under β*2 and β*1 at the expense of β2 and β1. Moreover, the total D coverage continuously decreases from ≃1.23 ML in the absence of B to ≃0.74 ML al θB=0.5 ML. We propose that the observed B-induced decrease in the Si*-D bond strength, where Si* represents surface Si atoms bonded to second-layer B atoms, is due to charge transfer and increased Si* dimer strain. The Si* to B charge transfer also deactivates Si surface dangling bonds causing the decrease in θD. These results are used to explain the GS-MBE growth kinetics.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)