  The electron transport in the two-dimensional gas formed in tensile-strained
Si1-xGex/Si/Si1-xGex heterostructures is investigated using Monte Carlo
simulation. At first the electron mobility is studied in ungated modulation
doped structures. The calculation matches very well the experimental results
over a wide range of electron density. The mobility typically varies between
1100 cm2/Vs in highly-doped structures and 2800 cm2/Vs at low electron density.
The mobility is shown to be significantly influenced by the thickness of the
spacer layer separating the strained Si channel from the pulse-doped supply
layers. Then the electron transport is investigated in a gated modulation-doped
structure in which the contribution of parasitic paths is negligible. The
mobility is shown to be higher than in comparable ungated structures and
dependent on the gate voltage, as a result of the electron density dependence
of remote impurity screening.
