The Power Factor of Bi2−x Tl x Se3 Single Crystals

Abstract

Single crystals of the ternary system Bi2−x Tl x Se3 (nominally x = 0.0 to 0.1) were prepared using the Bridgman technique. Samples with varying content of Tl were characterized by measurement of lattice parameters, electrical conductivity σ ⊥c, Hall coefficient R H(B║c), and Seebeck coefficient S(ΔT⊥c). The measurements indicate that incorporation of Tl into Bi2Se3 lowers the concentration of free electrons and enhances their mobility. This effect is explained within the framework of the point defects in the crystal lattice, with formation of substitutional defects of thallium in place of bismuth (TlBi) and a decrease in the concentration of selenium vacancies ( $$ V_{\rm{Se}}^{ + 2} $$ ). The temperature dependence of the power factor σS 2 of the samples is also discussed. As a consequence of the thallium doping we observe a significant increase of the power factor compared with the parent Bi2Se3.