Role of vacancies to p-type semiconducting properties of SiGe nanowires

Abstract

Many experiments have shown that both composition-randomly-distributed Si_1−xGe_x nanowires (NW) and the Ge/Si core/shell NW possess excellent p-type semiconducting properties without relying on any doping strategy. Vacancies in both NW are believed to play a key role in the p-type semiconducting properties. To gain deeper insights into the role of vacancies, we performed first-principle calculations to systematically study the effects of single Si or Ge vacancies in four distinct SiGe NW, namely, randomly-distributed triangular-prism (RTP) NW, fused triangular-prism (FTP) NW, the Ge_coreSi_shell NW and Si_coreGe_shell NW. We find that the tendency for vacancy formation depends strongly on the structures of the NW. The defective RTP, FTP and Ge_coreSi_shell NW show promising p-type semiconducting properties while the defective Si_coreGe_shell NW does not. The Si vacancies in the inner region are attributed to the p-type properties of the RTP NW, and both the Si and Ge vacancies at the core/shell interfaces are attributed to the p-type properties of the FTP and the Ge_coreSi_shell NW. Our results show how the vacancies affect the electronic structures and the semiconducting properties of different SiGe NW, and offer an explanation of why the synthesized Si_1−xGe_x and Ge_coreSi_shell NW possess excellent p-type semiconducting properties without relying on any doping strategy.