Thermoelectric properties of GeTe-based heterojunctions and its homojunction

In view of the important role played by the interlayer interactions in layered two-dimensional materials, we systematically investigate how the interlayer interactions affect the thermoelectric (TE) properties of the GeTe-based heterojunctions, as well as its homojunction. It is shown that the GeTe-based heterojunctions and homojunction XY/GeTe (X = Ge, Sn and Y = Te, Se, S) and PbTe/GeTe are all semiconductors with their bandgaps near chemical potential μ = 0 eV uniformly much smaller than the GeTe monolayer. However, the bandgap of about 0.3 eV above the first conduction band corresponding to the GeTe monolayer can be enlarged or even suppressed to vanish by the interlayer interactions and the adjoint layer. Therefore, the electronic transmission coefficients and the TE properties including the Seebeck coefficients, the power factors, the thermal conductances, and the figures of merit ZTs are all seriously changed by the presence of the heterojunctions or homojunction. Compared with the GeTe monolayer, the ZT peaks may increase or decrease in magnitude, while their positions shift toward μ = 0 eV. Thus, we have clearly elucidated the influences of the interlayer junctions on the TE properties, which also demonstrates a feasible way of manipulating the ZT of GeTe monolayer by the heterojunction or homojunction scheme. Moreover, the temperature dependence of the ZT peaks has also been explored.