The Thermoelectric Properties of -Type Bismuth Telluride: Bismuth Selenide Alloys
(a) Four band edges are primarily responsible for the electronic transport in the -type alloy system. The peak in the conduction band Seebeck effective mass near Bi2Te2.7Se0.3 occurs due to the crossing of the sixfold and twofold valleys. The loss of weighted mobility with increasing selenium content is attributable to the reduction in effective valley degeneracy due to the pocket rising far above the CBM and increasing in mass and the pocket transitioning from to 1 as the curvature inverts at due to the reduction in SOI-induced anticrossing. The peak in band gap near Bi2Te2Se can be understood as a crossing between the and valence band edges. This schematic can be used to fit a two-band effective mass model with weighted mobility and effective mass parameters as shown in (b). These parameters generate the dashed lines fit to transport data in Figure 2.