Thermoelectric properties of Tl‐doped Bi 2 Se 3 single crystals

The single crystals of the ternary system based on Bi 2‐x Tl x Se 3 (nominaly x = 0.0‐0.1) were prepared using the Bridgman technique. Samples with varying content of Tl were characterized by the measurement of lattice parameters, electrical conductivity σ ⊥ c , Hall coefficient R H ( B∥c ), and Seebeck coefficient S (Δ T ⊥ c ). The measurements indicate that by incorporating Tl in Bi 2 Se 3 one lowers the concentration of free electrons and enhances their mobility. This effect is explained in terms of the point defects in the crystal lattice – formation of substitutional defects thallium on the site of bismuth Tl Bi and the decrease of concentration of selenium vacancies V Se +2 . We also discuss the temperature dependence of the power factor σS 2 of the samples. Upon the thallium doping we observe a significant increase of the power factor compare to the parental Bi 2 Se 3 . (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)