Growth mode of epitaxial Si_0.5Ge_0.5 layer grown on Si(100) by ion-beam-assisted deposition

The nucleation and growth of the Si_0.5Ge_0.5 alloy layer on Si (100) substrate during ion-beam-assisted deposition (IBAD) have been investigated by atomic force microscopy, reflection high-energy electron diffraction, transmission electron microscopy, and double-crystal rocking diffraction. We confirmed that Si_0.5Ge_0.5 nucleates on Si (100) via the Stranski-Krastanov (SK) mechanism by IBAD, and Ar-ion bombardment suppressed SK growth mode as well as improved crystalline perfection. The epitaxial temperature was observed at 200 °C, and it was much lower than the growth temperature (550-600 °C) in molecular-beam epitaxy (MBE). The χ_min value (the ratio of channeling to random backscattering yields) was 10.5% lower than the obtained MBE value. The effect of ion bombardment on nucleation was explained as the result of ion-bombardment-induced dissociation of three-dimensional islands and enhanced surface diffusion, and appeared only at low deposition temperatures where the dissociation of three-dimensional islands is more favorable than the formation of those islands.