Effects of growth direction on sige/si heteroepitaxy

In this work we study the growth of SiGe/Si superlattices and thick SiGe layers on ( 1 00), ( 1 1 1 ),and ( 1 1 0) Si surfaces at various temperatures by molecular-beam epitaxy (MBE) . We find that these three growth directions give rise to different growth morphologies and defect structures. The best growth is achieved on (100) surfaces, since growth on ( 1 1 1 ) and ( 1 1 0) surfaces are much more susceptible to twin formation. The growth direction, together with growth temperature, also dictates the onset of long-range ordering in SiGe layers. Our results indicate that ordering occurs only in thick, partially-relaxed SiGe layers grown on (100) surfaces at low temperatures but not in strained-layer superlattices grown under identical conditions. Thick SiGe layers or strained-layer superlattices grown on (1 1 1) or (1 10) surfaces at high or low temperatures do not exhibit ordering.