Interactions between Functional Units Inducing the Evolution of Electronic Band Structure and Improved Thermoelectric Performance of n-Type (Bi₂)_x(Bi₂Te₃)_y Pseudosuperlattices

Abstract

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 (Bi 2 ) x (Bi 2 Te 3 ) 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 (Bi 2 ) x (Bi 2 Te 3 ) y films with rising Bi 2 content, which is attributed to the spontaneous electron injection from the Bi 2 layers to the Bi 2 Te 3 layers due to their work function difference. By angle-resolved photoemission spectroscopy measurements, we observed rich electronic band structures in Bi 2 -terminated (Bi 2 ) x (Bi 2 Te 3 ) y films, containing two sets of band dispersions: one originating from Bi 2 Te 3 and the other from the hybridization of Bi 2 states and Bi 2 Te 3 states, similar to those reported in Bi 1 Te 1 and Bi 4 Te 3 superlattices. In contrast, the band dispersions are dominated by the energy bands from the Bi 2 Te 3 compound when the Bi 2 Te 3 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 (Bi 2 ) 12 (Bi 2 Te 3 ) 6 pseudosuperlattice film achieved the highest power factor of 1.27 mW m −1 K −2 , surpassing the performance of pristine Bi 2 Te 3 and Bi films as well as other pseudosuperlattices. KEYWORDS: (Bi 2 ) x (Bi 2 Te 3 ) y , pseudosuperlattices, band structure, interlayer interactions, thermoelectric performance