A MODEL FOR THE HIGH-TEMPERATURE TRANSPORT-PROPERTIES OF HEAVILY DOPED N-TYPE SILICON-GERMANIUM ALLOYS

A model is presented for the high-temperature transport properties of large-grain-size, heavily doped n-type silicon-germanium alloys. Electron and phonon transport coefficients are calculated using standard Boltzmann equation expressions in the relaxation time approximation. Good agreement with experiment is found by considering acoustic phonon and ionized impurity scattering for electrons, and phonon-phonon, point defect, and electron-phonon scattering for phonons. The parameters describing electron transport in heavily doped and lightly doped materials are significantly different and suggest that most carriers in heavily doped materials are in a band formed largely from impurity states. The maximum dimensionless thermoelectric figure of merit for single-crystal, n-type Si0.8Ge0.2 at 1300 K is estimated at ZT congruent-to 1.13 with an optimum carrier concentration of n congruent-to 2.9 x 10(20) cm-3.