The influence of hydrogen during the growth of Ge films on Si(001) by solid source molecular beam epitaxy

We examine here the effect of adsorbed atomic hydrogen (H) in the earliest stages of Ge film growth on a Si(001) substrate by solid source molecular beam epitaxy (MBE). Contrary to the gas source MBE or CVD methods, the use of a H flux, generated by hot filament dissociation, allows us to separate I-I and Ge supplies. In a low substrate temperature range between 100 and 350 degrees C, we clearly observe a growth mode evolution by in-situ reflection high-energy electron diffraction (RHEED). Especially at 300 degrees C, a change from the well-known Stranski-Krastanov (SK) mode without H to a layer-by-layer growth mode with H is evidenced. The presence of H at the growing surface indeed extends the RHEED intensity oscillations at Ge coverages well above the SK critical thickness and prevents island formation. Rather thick epitaxial Ge layers (up to 55 ML) present a persisting 2D growth with weak roughness and a reduced strain relief as revealed by RHEED in-plane lattice parameter measurements. (C) 1998 Elsevier Science B.V. All rights reserved.