Thermoelectric Properties of Cu-Doped n-Type Bi^sub 2^Te^sub 2.85^Se^sub 0.15^ Prepared by Liquid Phase Growth Using a Sliding Boat

Issue Title: 2014 International Conference on Thermoelectrics. Guest Editors: Lasse Rosendahl, Donald Morelli, Jihui Yang, Hiroaki Anno, Matt Beekman, Jan D. Koenig, Xinfeng Tang, James R. Salvador, Bertrand Lenoir, Chunlei Wan, Jeff Sharp, Emmanuel Guilmeau, Hsin Wang, Jing-feng Li, Tie-Jun Zhu, David Singh, Ryoji Funahashi, Yuri Grin, and Wenqing Zhang N-type Bi^sub 2^Te^sub 2.85^Se^sub 0.15^ thermoelectric materials were prepared by liquid phase growth (LPG) using a sliding boat, a simple and short fabrication process for Bi^sub 2^Te^sub 3^-related materials. Cu was selected as a donor dopant, and its effect on thermoelectric properties was investigated. Thick sheets and bars of Cu^sub x^Bi^sub 2^ Te^sub 2.85^Se^sub 0.15^ (x=0-0.25) of 1-2mm in thickness were obtained using the process. X-ray diffraction patterns and scanning electron micrographs showed that the in-plane direction tended to correspond to the hexagonal c-plane, which is the preferred direction for thermoelectric conversion. Cu-doping was effective in controlling conduction type and carrier (electron) concentration. The conduction type was p-type for undoped Bi^sub 2^Te^sub 2.85^Se^sub 0.15^ and became n-type after Cu-doping. The Hall carrier concentration was increased by Cu-doping. Small resistivity was achieved in Cu^sub 0.02^Bi^sub 2^Te^sub 2.85^Se^sub 0.15^ owing to an optimized amount of Cu-doping and high crystal orientation. As a result, the maximum power factor near 310K for Cu^sub 0.02^Bi^sub 2^Te^sub 2.85^Se^sub 0.15^ was approximately 4×10^sup -3^W/K^sup 2^m and had good reproducibility. Furthermore, the thermal stability of Cu^sub 0.02^Bi^sub 2^Te^sub 2.85^Se^sub 0.15^ was also confirmed by thermal cycling measurements of electrical resistivity. Thus, n-type Bi^sub 2^Te^sub 2.85^Se^sub 0.15^ with a large power factor was prepared using the present LPG process.