Abstract
We report thermopower measurements in zero and low magnetic fields for a p-type Si/Si1-xGex heterostructure. The diffusion components of both the longitudinal and transverse components are reasonably well described by the Mott approach, including the quantum oscillations at low magnetic fields. The magnetic-field dependence of thermopower shows that the diffusion contribution at zero field deviates from the linear temperature dependence that would be expected for a degenerate system, probably as a result of the nearby metal-insulator transition. Phonon drag also does not behave as expected. Instead of exhibiting an approximate T-6 dependence at low temperatures appropriate to screened, hole-phonon, deformation-potential scattering, an approximate T-4 dependence is observed. This is consistent with previous observations on the energy-loss rates in SiGe hole systems. The experimental data on drag are in good agreement with numerical calculations by assuming either hole-phonon scattering by an unscreened deformation-potential interaction or by assuming a screened piezoelectric plus screened deformation-potential coupling.
