Exceptionally high thermoelectric power factors at low temperatures in heavily doped p- and n-type Ge-rich Ge1−xSnx films

Low-temperature thermoelectric thin films compatible with semiconductor technology are of increasing interest for cryogenic energy harvesting and thermal management of advanced Si-based electronics. Here, we show that heavily doped p- and n-type Ge1−xSnx epitaxial films exhibit exceptionally high thermoelectric power factors (PF) at low temperatures owing to a pronounced phonon-drag effect. Hall-effect and Seebeck-effect analyses over a wide temperature range of 6–300 K reveal that this phonon-drag contribution, manifested as a strong enhancement of the Seebeck coefficient at low temperatures, persists even at high carrier concentrations approaching 1020 cm−3. Along with the simultaneous increase in electrical conductivity upon cooling, the PFs rise dramatically, reaching 1.4 × 102 and 4.7 × 103 μWcm−1 K−2 around 20 K for the p- and n-type films, respectively. These remarkably high PFs enhanced by phonon-drag effect demonstrate that heavily doped Ge1−xSnx provides a promising platform for low-temperature group-IV thin-film thermoelectrics.