Influence of In Doping on the Electronic Transport Properties of n-Type Cu _0.008 Bi ₂ Te _2.7 Se _0.3

Doping is an effective approach to enhance the thermoelectric figure of merit (zT) of thermoelectric alloys by modifying their electronic structure. In this study, we investigated the influence of In doping on the electronic and thermal transport properties of n-type Cu ₀₀₀₈ Bi _2-x In _x Te _2.7 Se _0.3 (x = 0, 0.005, 0.01, and 0.015) polycrystalline alloys. The electrical conductivity of the alloys showed a moderate decreased by In doping. The Seebeck coefficient also decreased slightly. The bandgap E _g of the alloys widened slightly according to the Goldsmid–Sharp E _g formula. The band parameters of the conduction and valence bands were estimated using a two-band model. In the case of the In-doped samples, the concentration and mobility of electrons decreased simultaneously, resulting in a reduction in the electrical conductivity. However, the level of bipolar conduction remained unchanged even after doping because of the compensation of E _g widening and the band parameter modification. Meanwhile, the effect of In doping on the thermal conductivity of n-type Cu _0.008 Bi ₂ Te _2.7 Se _0.3 was found to be insignificant. Consequently, the zT of the alloy increased slightly to 1.12 at x = 0.05, while it decreased at higher doping levels.