Electron drift mobility in a Si-${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ quantum well at low temperatures

The electron drift mobility in a Si-${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Si}}_{\mathit{x}}$ quantum well at low temperatures is calculated by means of a standard Boltzmann-transport-equation approach in the relaxation-time approximation. Conduction along the Si channel is considered and two scattering mechanisms are discussed: acoustic phonons via deformation-potential coupling and ionized impurities. The role of acoustic phonons is analyzed to be rather important in order to achieve agreement with experimental measurements. All the calculations are done in the quantum size limit and just the first subband is assumed to contribute to electron conduction.