Studies of the Initial Growth of (100) Heterostructures Silicon/germanium/silicon

The initial growth of Si on Ge strained ultra -thin film grown on Si(100) has been investigated by in -situ Reflection High Energy Electron Diffraction (RHEED) and quantitative Auger Electron Spectroscopy (AES) in a Ultra-High Vacuum (UHV) system. Ge layers of 1,2,3, and 4 monolayers (ML) were grown on Si(100) substrate at 600 ^circ{rm C}, and Si overlayers of 20 to 40ML were deposited at room temperature with post-deposition annealing, and at intermediate temperatures from 250 to 520^circ {rm C}. In this set of experiments, Ge surface segregation and Ge-Si interdiffusion during annealing were both studied. Well structured 2*1 and 2*n RHEED patterns indicated a layer-by-layer growth mode during Si overlayer deposition on strained Ge/Si(100), which differs from the island growth mode of Si on bulk Ge. Persistent 2*n structures after several atomic layers of Si deposition were observed. Ge LMM 1140eV peaks were analyzed by quantitative AES data analysis. Both AES and RHEED indicated more than 90% Ge surface segregation under equilibrium conditions depending on the Ge interlayer thickness. By applying a two-site exchange model to the segregation probability derived from the AES analysis, the segregation energy was determined to be 0.24 +/- 0.02eV, which is dependent on the Ge interlayer thickness as well. RHEED patterns obtained during Si overlayer deposition indicate that the initially rough surface due to the Ge interlayer deposition became smooth after a few overlayers of Si deposition. A growth mechanism of Si on strained Ge/Si(100) thin film is proposed to interpret this experimental observation, and the surface roughness has been included in the computer model for quantitative AES analysis.