First-Principles Study of All Thermoelectric Properties of Si-Ge Alloys Showing Large Phonon Drag from 150 to 1100 K

Abstract

Phonon drag due to momentum exchange between electrons and phonons can lead to a substantially increased Seebeck coefficient desirable for thermoelectric energy conversion. However, this effect is only usually observable at low temperatures when the phonon mean free path is long, and it is thought to become negligible above room temperature or in heavily doped materials due to strong phonon scattering. Here, we present first-principles calculations of all thermoelectric transport properties of silicon-germanium alloys from 150 to 1100 K. Results show that phonon drag is dominant at low temperatures. At 1100 K, phonon drag still contributes to 10%–20% of the thermoelectric figure of merit, zT, and its relative contribution increases with higher carrier concentration. The favorable comparison between our calculations and reported experiments brings us closer to predicting the thermoelectric transport properties of alloys using first-principles simulations. The surprising insights in phonon drag could stimulate the search for better thermoelectric materials.