Roughening of SiGe layers grown with gas-source MBE: dependence on Ge concentration and growth temperature

Abstract

We have investigated the roughening of SiGe layers grown from disilane and germane on Si(001) using gas-source molecular beam epitaxy (GSMBE). Si 1 − x Ge x layers were grown in the temperature range of 500–650°C while the Ge concentration x was varied between 0.06–0.28. Photoluminescence spectroscopy (PL) was used to calibrate the Ge concentration in SiGe layers. During growth the SiGe surfaces were inspected with reflection high-energy electron diffraction (RHEED) and after deposition with scanning electron microscopy (SEM). At low temperatures and Ge concentrations we found smooth (2D) layers. However, for high temperatures and Ge concentrations we obtained rough {118} and {113} faceted layers (3D). Comparison with solid-source MBE (SSMBE) results (Bean et al. [J. Vac. Sci. Technol. A 2 (1984) 436]) reveal that 3D growth in GSMBE is observed for lower Ge concentrations and temperatures. This difference can be explained by the much lower growth rates used in our experiments. At higher growth rates the surface atom diffusion length is reduced and the development of the thermodynamically favourable 3D phase is suppressed.