Influence of trigonal deformation on band structure and Seebeck coefficient of tellurium

Abstract

Effects of trigonal deformation (c/a) on electronic structure and Seebeck coefficient of tellurium have been studied using first principles calculation combined with Boltzmann transport theory. Tellurium is found to be an indirect-gap semiconductor when 1.174 ≤ c/a<1.274, a direct-gap semiconductor when 1.274 ≤ c/a≤1.372, and a typical semimetal when 1.372 < c/a ≤1.444. Moreover, a semiconductor-semimetal transition of tellurium is discovered at the critical c/a of 1.372, which is mainly because of the transition of the conduction band bottom and valence band top near the high-symmetry point of H. Calculations also reveal the significant impact of trigonal deformation on the Seebeck coefficient of tellurium, i.e., the highest Seebeck coefficient of tellurium can be achieved at the c/a ratio of 1.274, and seems much better than that of equilibrium tellurium (c/a = 1.324). The present calculated results agree well with experimental measurements and theoretical predictions and could provide in-depth understanding of the intrinsic relationship among trigonal deformation, electronic band structure, semiconductor-semimetal transition, and Seebeck coefficient of tellurium.