Role of vacancies to p-type semiconducting properties of SiGe nanowires†
Many experiments have shown that both composition-randomly-distributed Si1−xGex 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 GecoreSishell NW and SicoreGeshell NW. We find that the tendency for vacancy formation depends strongly on the structures of the NW. The defective RTP, FTP and GecoreSishell NW show promising p-type semiconducting properties while the defective SicoreGeshell 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 GecoreSishell 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 Si1−xGex and GecoreSishell NW possess excellent p-type semiconducting properties without relying on any doping strategy.