Smear-out of the Ge/Si Interface in Gas Source MBE Monitored by Rheed

Abstract

We have studied the growth of Si layers on very thin (≈ 1 monolayer) Ge films, which were deposited on Si (100) substrates in gas source molecular beam epitaxy (GSMBE) using disilane and germane, respectively. Reflection high energy electron diffraction (RHEED) intensity oscillation traces recorded during the growth of silicon on these layers showed a strong increase in growth rate for the first monolayers and a subsequent return to the value for the homoepitaxial Si on Si growth for substrate temperatures lower than 550°C. The rate at which the growth rate returns to the value for pure Si on Si depends on the actual growth temperature. Since hydrogen desorption is the rate limiting step in the deposition of Si on Si, we suggest that Ge at the surface enhances the hydrogen desorption rate in GSMBE, with the observed higher silicon growth rate as a consequence. Furthermore, the decay rate as indicated by the RHEED oscillations indicates a continuously diminishing concentration of Ge at the surface of the growing layer. Angle resolved X-ray photoelectron emission spectroscopy (ARXPS) shows that a part of the “floating” Ge is incorporated into the growing Si layer, leading to a smear-out of the Ge/ Si heterointerface