Transport properties of two-dimensional electron systems on silicon   (111) surfaces
  We theoretically study transport properties of a two-dimensional electron system on a hydrogen-passivated Si(111) surface in the field-effect-transistor (FET) configuration. We calculate the density and temperature dependent mobility and resistivity for the recently fabricated Si(111)-vacuum FET by using a semiclassical Boltzmann theory including screened charged impurity scattering. We find reasonable agreement with the corresponding experimental transport properties, indicating that the screened disorder potential from random charged impurities is the main scattering mechanism. We also find that the theoretical results with the valley degeneracy $g_v=2$ give much better agreement with experiment than the $g_v=6$ situation indicating that the usual bulk six-valley degeneracy of Si is lifted in this system. 
E. H. Hwang and S. Das Sarma