A Reflection High-Energy Electron-Diffraction Study Of The Si(111) Surface During Gas Source Molecular-Beam Epitaxy

Reflection high-energy electron diffraction was used to monitor Si(111) growth during gas source molecular beam epitaxy using disilane (Si2H6). Depending on the substrate temperature, the growing Si(111) surface was found to exhibit hydrogenated delta(7 x 7), (1 x 1), (5 x 5), and (7 x 7) reconstructions. Within the substrate temperature range of 490 to 560-degrees-C where growth proceeded two-dimensionally, clear and well-defined intensity oscillations could be observed in the [211BAR] and [110BAR] azimuths. Since consecutive atomic layers on the Si(111) surface are nonequivalent, the oscillation periods were found to correspond to bilayer growth. In the two-dimensional (2D) growth regime, the oscillation frequencies, and hence the growth rates deduced, were found to increase with increasing substrate temperature and flow rate of Si2H6. At higher temperatures, there was a change from 2D layer-by-layer growth to step propagation and consequently, the intensity oscillations were weak or absent. At low temperatures (< 400-degrees-C) where no dissociative adsorption of Si2H6 occurred, intensity oscillations were not observed.