Interactions between Functional Units Inducing the Evolution of Electronic Band Structure and Improved Thermoelectric Performance of n-Type (Bi₂)_<i>x</i>(Bi₂Te₃)_<i>y</i> Pseudosuperlattices

An ordered construction of functional units is a promising avenue to synergistically optimize the electrical and thermal transport properties of superlattices and pseudosuperlattices. Although it is accepted that interlayer interactions between functional units could effectively regulate carrier transport parameters, the influence of artificial stacking modalities on electronic band structures and thermoelectric performance required in-depth studies. Here, we report the fabrication of two batches of n-type (Bi2)x(Bi2Te3)y pseudosuperlattice films with varying thicknesses and termination surfaces. An obvious downshift of the Fermi level position and a remarkable increase of the electron density were observed in the (Bi2)x(Bi2Te3)y films with rising Bi2 content, which is attributed to the spontaneous electron injection from the Bi2 layers to the Bi2Te3 layers due to their work function difference. By angle-resolved photoemission spectroscopy measurements, we observed rich electronic band structures in Bi2-terminated (Bi2)x(Bi2Te3)y films, containing two sets of band dispersions: one originating from Bi2Te3 and the other from the hybridization of Bi2 states and Bi2Te3 states, similar to those reported in Bi1Te1 and Bi4Te3 superlattices. In contrast, the band dispersions are dominated by the energy bands from the Bi2Te3 compound when the Bi2Te3 layers are the termination surfaces. Moreover, the thinner films showed higher electron density and carrier effective mass due to the suppression of p-type BiTe antisite defects. Finally, the (Bi2)12(Bi2Te3)6 pseudosuperlattice film achieved the highest power factor of 1.27 mW m–1 K–2, surpassing the performance of pristine Bi2Te3 and Bi films as well as other pseudosuperlattices.