Interactions between Functional Units Inducing the Evolution of Electronic Band Structure and Improved Thermoelectric Performance of n-Type (Bi2)x(Bi2Te3)y 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 Bi_Te 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.