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학술지 Ultrafast Photocarrier Dynamics Related to Defect States of Si1_xGex Nanowires Measured by Optical Pump-THz Probe Spectroscopy
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저자
배정민, 이우정, 정성훈, 마진원, 정광식, 오승훈, 김성신, 서동찬, 송우빈, 김선정, 박재헌, 조만호
발행일
201706
출처
Nanoscale, v.9 no.23, pp.8015-8023
ISSN
2040-3364
출판사
Royal Society of Chemistry (RSC)
DOI
https://dx.doi.org/10.1039/c7nr00761b
협약과제
16PB2200, 초경량 유연 CIGS 박막 모듈 공정장비 상용화 기술개발, 정용덕
초록
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 -?봗/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.
KSP 제안 키워드
Charged states, Fitting formula, Ge content, Indirect semiconductors, Interface defect states, Photo-excited, Physical model, Substoichiometric oxide, Time Scale, Vapor-liquid-solid, band structure