Hole transport in SiGe channels on step-bunched vicinal Si surfaces

Hole transport in narrow modulation doped Si1−xGex channels grown on vicinal Si(1 1 3) by molecular beam epitaxy is studied. Owing to the strong step-bunching properties of the Si(1 1 3) surface, the Si1−xGex channels exhibit regular terraces with a width of typical View the MathML source and a mean step height of View the MathML source, corresponding to 25 monolayers, when appropriate growth conditions are used. Considerable amount of Si1−xGex material accumulates at the step edges resulting in regular wire-like channel thickness variations. At low temperatures, we find a pronounced resistivity anisotropy for transport perpendicular and parallel to the step edges. The resistivity is maximum for the current flow perpendicular to the step edges. This can be explained by a lateral modulation of the hole confinement potential caused by the channel thickness variation near the step edges. Lowering the doping concentration, i.e. decreasing the effective carrier density in the channel, enhances the resistivity anisotropy up to ρ⊥/ρ||≈16. We attribute this to an increasing resistivity of depleted SiGe layer regions in between the wire-like structures, when the Fermi energy gets comparable to the lateral potential barriers.