Wu Lihua, Yang Jiong, Zhang Tiansong, Wang Shanyu, Wei Ping, Zhang Wenqing, Chen Lidong, Yang Jihui
State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, People's Republic of China. Materials Science and Engineering Department, University of Washington, Seattle, WA 98195, USA. Materials Genome Institute, Shanghai University, Shanghai 200444, People's Republic of China.
J Phys Condens Matter. 2016 Mar 2;28(8):085801. doi: 10.1088/0953-8984/28/8/085801. Epub 2016 Feb 1.
Rashba semiconductors are of great interest in spintronics, superconducting electronics and thermoelectrics. Bulk BiTeI is a new Rashba system with a giant spin-split band structure. 2D-like thermoelectric response has been found in BiTeI. However, as optimizing the carrier concentration, the bipolar effect occurs at elevated temperature and deteriorates the thermoelectric performance of BiTeI. In this paper, band gap engineering in Rashba semiconductor BiTeI through Br-substitution successfully reduces the bipolar effect and improves the thermoelectric properties. By utilizing the optical absorption and Burstein-Moss-effect analysis, we find that the band gap in Rashba semiconductor BiTeI increases upon bromine substitution, which is consistent with theoretical predictions. Bipolar transport is mitigated due to the larger band gap, as the thermally-activated minority carriers diminish. Consequently, the Seebeck coefficient keeps increasing with a corresponding rise in temperature, and thermoelectric performance can thus be enhanced with a ZT = 0.5 at 570 K for BiTeI0.88Br0.12.
Rashba半导体在自旋电子学、超导电子学和热电学领域备受关注。块状BiTeI是一种具有巨大自旋分裂能带结构的新型Rashba体系。在BiTeI中发现了类似二维的热电响应。然而，随着载流子浓度的优化，在高温下会出现双极效应，从而降低了BiTeI的热电性能。本文通过Br取代对Rashba半导体BiTeI进行带隙工程，成功降低了双极效应并改善了热电性能。通过利用光吸收和Burstein-Moss效应分析，我们发现Rashba半导体BiTeI中的带隙在溴取代后增大，这与理论预测一致。由于带隙增大，热激活的少数载流子减少，双极输运得到缓解。因此，塞贝克系数随温度升高持续增加，对于BiTeI0.88Br0.12，在570 K时热电性能可通过ZT = 0.5得到增强。
