Alloy scattering limited transport of two-dimensional carriers in strained Si_1-xGe_x quantum wells

The mobility of two-dimensional electron systems in strained Si _1-xGe_x quantum wells was studied at low temperatures as a function of the germanium content in the well. While mobilities exceeding 30 000 cm²/V s have been achieved for pure Si layers, they dropped to less than 3000 cm²/V s for Si_0.88Ge_0.12 wells, demonstrating the effect of strong alloy disorder scattering. This was confirmed by the relatively weaker dependence of mobility on carrier concentration in gating experiments. By accounting for valley degeneracy effects in the standard two-dimensional alloy scattering model, an effective scattering potential V _alloy=0.8±0.1 eV has been derived for electrons. Using a weaker potential, it is shown that the maximum low temperature mobilities for holes reported in literature are also consistent with the alloy scattering model.