Systematic studies of SiGe∕Si islands nucleated via separate in situ or ex situ Ga+ focused ion beam-guided growth techniques

In this study, we use 25 keV in situ and 30 keV ex situ Ga+ focused ion beams (FIBs) to locally modify the substrate before deposition and determine their effects on nucleation of molecular beam epitaxy grown Ge∕Si islands. FIB processing may alter island formation in at least five ways: the surfactant effect of Ga+, doping effects of subsurface Ga+, local strains, crystalline damage, and surface roughening. To explore these possibilities, we milled square regions of increasing Ga+ doses and used atomic force microscopy to monitor islanding in and around these regions. For in situ experiments, doses ranged from ∼1013 to 5×1017ions∕cm2 (0.04–400 ML). We began to observe changes in island topology at doses as low as ∼1014ions∕cm2. For doses of ∼1015 to ∼8×1016ions∕cm2 (2–160 ML), implanted areas were surrounded by denuded zones that grew from ∼0.5 to 6μm with increasing dose. Immediately inside the implanted area, island size and concentration appeared to peak. At doses above ∼6×1016ions∕cm2 (120 ML), Ga+ p...