Important role of Cu in suppressing bipolar conduction in Bi-rich (Bi,Sb)(2)Te-3

Abstract

Cu doping has been known to enhance thermoelectric performance of p-type (Bi,Sb)(2)Te-3 alloys by suppressing bipolar conduction at higher temperatures. However, detailed mechanisms are not provided yet. Herein, we investigate the unchallenged role of Cu doping in (Bi,Sb)(2)Te-3 alloys by means of Bi-rich compositions of Bi0.6Sb1.4Te3 and Bi0.7Sb1.3Te3, which were chosen since they exhibit much inferior thermoelectric performance owing to severe bipolar conduction. It was found that Cu doping increases non-degenerate mobility and density-of-states effective mass of valence band as well as hole concentration. Small amount of Cu doping enhanced maximum thermoelectric figure-of-merit of Bi0.6Sb1.4Te3 composition from 0.25 to 0.98. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights