  Scattering rate calculations in two-dimensional Si/SiGe systems have
typically been restricted to rectangular Ge profiles at interfaces between
layers. Real interfaces, however, may exhibit diffuse Ge profiles either by
design or as a limitation of the growth process. It is shown here that alloy
disorder scattering dramatically increases with Ge interdiffusion in (100) and
(111) n-type quantum wells, but remains almost constant in (100) p-type
heterostructures. It is also shown that smoothing of the confining potential
leads to large changes in subband energies and scattering rates, and a method
is presented for calculating growth process tolerances.
