SURFACE SEGREGATION AND GROWTH-MODE TRANSITIONS DURING THE INITIAL-STAGES OF SI GROWTH ON GE(001)2X1 BY CYCLIC GAS-SOURCE MOLECULAR-BEAM EPITAXY FROM SI2H6

Surface morphological and compositional evolution during the initial stages of Si growth on Ge(001)2X1 by cyclic gas-source molecular beam epitaxy from Si2H6 has been investigated using in situ reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy, electron-energy-loss spectroscopy, and scanning tunneling microscopy, combined with post-deposition high-resolution cross-sectional transmission electron microscopy. The layers were deposited using repetitive cycles consisting of saturation Si2H6 dosing at room temperature, followed by annealing for 1 min at 550 degrees C. Film growth was observed to proceed via a mixed Stranski-Krastanov mode. Single-step-height two-dimensional growth was obtained for nominal Si deposition thicknesses t(si) up to similar or equal to 1.5 monolayers (ML). However, the upper layer remained essentially pure Ge which segregated to the surface through site exchange with deposited Si as H was desorbed. At higher tsi, the Ge coverage decreased slowly, the surface roughened, and two-dimensional multilayer island growth was observed for rsi up to similar or equal to 7.5 ML, where bulk reflections in RHEED patterns provided evidence for the evolution of three-dimensional island formula.