Si:SiGe quantum wells grown on (118) substrates: Surface morphology and transport properties

We have grown strained Si quantum wells on relaxed Si0.7Ge0.3 buffer layers using vicinal (118) silicon substrates. Compared to conventional (001) substrates the surface is tilted by 10 degrees towards the [110] direction resulting in terraces with step edges which run parallel to [1(1) over bar0$]. The surface morphology of the layers shows ''cross-hatching'' characteristic of relaxed SiGe films grown on Si substrates. However, the cross-hatching is not orthogonal but aligns along directions in which (111) planes intersect the (118) surface. We have measured the low temperature transport properties of the two-dimensional electron gas confined within the strained Si channel. When measured with current flowing parallel to the step edges the electron mobility is approximately four times larger than that measured in a perpendicular direction showing the strong elastic scattering associated with the step edges. In contrast the single particle relaxation time is almost identical for the two different orientations. (C) 1997 American Institute of Physics.