Investigation of Si_mGe_n strained monolayer superlattices by Rheed, Raman, and X-ray techniques

Ultrathin Si_mGe_n strained monolayer superlattices (SMS) have been grown by molecular beam epitaxy. The critical thickness of the total superlattice is determined in situ by direct observation of the changes of surface reconstruction patterns using reflection high energy electron diffraction. Results are in close agreement with that of a single layer with the same thickness and the average SMS composition. Raman scattering and X-ray diffraction spectroscopy are used to study the thermal stability and surface abruptness. Subsequent annealing of these SMSs reveals that the transition from pure silicon and/or germanium layers to Si_1-xGe_x alloys becomes more pronounced as the annealing time and temperature are increased. The interdiffusion coefficients obtained from the X-ray spectrum are found to obey an Arrhenius relation with an activation energy of 3.1 ± 0.2 eV.