Enhancement of thermoelectric power factor in CaGe2 films through interlayer atomic modulation

Group IVA elements Si and Ge and their compounds possess abundant natural distribution and excellent electrical properties that are widely utilized in Si-based technology. The exploration for potentially high-performance thermoelectric materials within the Group IVA elements is a viable pursuit. In this work, Ca intercalated Germanene-CaGe2 films were grown on sapphire substrates by molecular beam epitaxy. It is found that the partial lack of Ca between the germanene buckled layers effectively increases the Seebeck coefficient without restraining the conductivity. A maximum power factor of 170 μW/mK2 at 523 K, which is seven times larger than the stoichiometric CaGe2 film, was achieved in the Ca0.835Ge2 film by suppression of bipolar effect and formation of a Ca-deficient phase. This study presents a promising approach to tuning the thermoelectric properties of layered semimetal materials through interlayer atomic modulation, which induces the buckled structure of the framework layer, thereby modifying the electronic structure.