In-situ monitoring of Si and SiGe growth on Si(001) surfaces during gas-source molecular beam epitaxy using reflectance anisotropy

Abstract

Reflectance anisotropy (RA) and reflection high energy electron diffraction (RHEED) were used simultaneously to study the growth of Si and SiGe on Si(001) surfaces by gas-source molecular beam epitaxy (GSMBE). These surfaces are dimerised and have a domain structure created by the orthogonal alignment of dimers on terraces separated in height by a 0 4 . Comparison between the RA and RHEED measurements reveals the origin of dynamic changes in the RA response to be the periodic changes in domain coverages on singular surfaces caused by growth under a monolayer-by-monolayer mode. It also demonstrates that RA is a more direct measure of domain coverage variations on the Si(001) surface compared with RHEED, which may suffer from effects of ordering and multiple scattering. The RA technique is used to investigate domain coverage variations as a function of temperature and following growth interruption. It is shown that there is no significant change in the domain coverage at 600°C during growth interruption, consistent with Monte Carlo simulation. This is despite the occurrence of migration of adatoms/islands as indicated by the recovery of specular beam intensity during simultaneous RHEED measurements. The temperature dependence of the dynamic change in RA response is interpreted as a growth mode change at high temperatures and change in the electronic configuration of the dimers due to chemisorbed hydrogen at low temperatures. The changes in the RA response during deposition of SiGe are also investigated as a function of Ge concentration at 600°C growth temperature.