Slightly tapered Si1-xGex nanowires (NWs) (x = 0.29-0.84) were synthesized via a vapor-liquid-solid procedure using Au as a catalyst. We measured the optically excited carrier dynamics of Si1-xGex NWs as a function of Ge content using optical pump-THz probe spectroscopy. The measured -ΔT/T0 signals of Si1-xGex NWs were converted into conductivity in the THz region. We developed a fitting formula to apply to indirect semiconductors such as Si1-xGex, which explains the temporal population of photo-excited carriers in the band structure and the relationship between the trapping time and the defect states on an ultrafast time scale. From the fitting results, we extracted intra- and inter-valley transition times and trapping times of electrons and holes of Si1-xGex NWs as a function of Ge content. On the basis of theoretical reports, we suggest a physical model to interpret the trapping times related to the species of interface defect states located at the oxide/NW: substoichiometric oxide states of Si(Ge)0+,1+,2+, but not Si(Ge)3+, could function as defect states capturing photo-excited electrons or holes and could determine the different trapping times of electrons and holes depending on negatively or neutrally charged states.
Bibliographical noteFunding Information:
This work was partially supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (Grant No. 2015R1A2A1A01007560) and partially supported by an Industry Academy joint research program between Samsung Electronics Yonsei University. The authors are grateful for the valuable help in the experiments performed using the fs-THz spectroscopy beamlines at the Pohang Light Source (PLS).
© 2017 The Royal Society of Chemistry.
All Science Journal Classification (ASJC) codes
- Materials Science(all)