TRANSPORT-PROPERTIES OF N-CHANNEL SI SIGE MODULATION-DOPED SYSTEMS WITH VARIED CHANNEL THICKNESS - EFFECT OF THE INTERFACE ROUGHNESS/

The effect of the interface roughness on the transport properties of m odulation-doped strained Si on relaxed Si0.8Ge0.2 is studied. The mobi lity decreases between 25 K and 300 K with decreasing channel thicknes s from 200 to 13 Angstrom. When the channel is thicker than 53 Angstro m, back-gated measurements reveal that the mobility is proportional to the carrier density, reflecting the two-dimensionality of the system. When the channel width is about 40 Angstrom, however, interface-rough ness scattering is found to strictly limit the mobility below 20 K fro m the temperature dependence as well as the thickness dependence of th e mobility. The vertical and lateral correlation lengths of the roughn ess are estimated to be 6.5-8.0 Angstrom and 120-130 Angstrom respecti vely. In the samples with a channel thickness less than 27 Angstrom, w hich is comparable to the roughness, it is found that a two-dimensiona l variable-range hopping process dominates the conductivity below 40 K .