High mobility two-dimensional hole system on hydrogen-terminated silicon   (111) surfaces
  We have realized a two-dimensional hole system (2DHS), in which the 2DHS is induced at an atomically flat hydrogen-terminated Si(111) surface by a negative gate voltage applied across a vacuum cavity. Hole densities up to $7.5\times10^{11}$ cm$^{-2}$ are obtained, and the peak hole mobility is about $10^4$ cm$^2$/Vs at 70 mK. The quantum Hall effect is observed. Shubnikov-de Haas oscillations show a beating pattern due to the spin-orbit effects, and the inferred zero-field spin splitting can be tuned by the gate voltage. 
Binhui Hu, Tomasz M. Kott, Robert N. McFarland and B. E. Kane
cond-mat.mes-hall cond-mat.mtrl-sci