Enhanced thermoelectric properties in multilayer-modulated GeTe/Sb2Te3 films

In this work, by modulating the stacking period of the individual GeTe and Sb₂Te₃ layers, a balance between electrical conductivity and Seebeck coefficient can be achieved to maximize the thermoelectric efficiency through the synergistic effect of material design flexibility and interface engineering. The coupling of acoustic and optical branches in the phonon dispersion of Sb₂Te₃, along with the presence of multi-carrier pockets in the band structure of GeTe, offers theoretical support for constructing a multilayer structure. The multilayer films sustain the two-phase structure composed of Sb₂Te₃ and GeTe phases. As the period number increases, there is an increase in optical band gap and carrier concentration, and a decrease in resistivity. The layered interface and nanocrystalline boundary inside the multilayer films are important scattering sources and significantly reduce the carrier mobility. In addition, nano-multilayer films modulate the carrier concentration to maintain an optimal order of 10¹⁹∼10²⁰ cm⁻³. The maximum power factor of GeTe/Sb₂Te₃ multilayer films obtained is 1081 μW/mK² at 473 K for single-period film. The power factor unexpectedly decreases as the number of periods in the film increases, which could be attributed to the enhanced thickness leading to higher carrier concentration and reduced nano scale effect.