A Model for the High Temperature Transport Properties of Heavily Doped P-Type Silicon-Germanium Alloys

ABSTRACTA model is presented for the high temperature transport properties of large grain size, heavily doped p-type silicon-germanium alloys. Good agreement with experiment (±10%) is found by considering acoustic phonon and ionized impurity scattering for holes and phonon-phonon, point defect and hole-phonon scattering for phonons. Phonon scattering by holes is found to be substantially weaker than phonon scattering by electrons, which accounts for the larger thermal conductivity values of ptype silicon-germanium alloys compared to similarly doped n-type silicongermanium alloys. The relatively weak scattering of long-wavelength phonons by holes raises the possibility that p-type silicon-germanium alloys may be improved for thermoelectric applications by the addition of an additional phonon scattering mechanism which is effective on intermediate and long-wavelength phonons. Calculations indicate improvements in the thermoelectric figure of merit up to 40% may be possible by incorporating several volume percent of 20 Å radius inclusions into p-type silicon-germanium alloys.