Ultrafast terahertz conductivity of photoexcited nanocrystalline silicon
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The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described by a classical Drude–Smith model, suitable for disorder-driven metal–insulator transitions. In this work, we explore the time evolution of the frequency dependent complex conductivity after optical injection of carriers on a picosecond time scale. Furthermore, we show the lifetime of photoconductivity in the silicon nanocrystal films is dominated by trapping at the Si/SiO2 interface states, occurring on a 1–100 ps time scale depending on particle size and hydrogen passivation.
KeywordsOptical Injection Picosecond Time Scale Photoconductive Decay Smith Model Energy Filter Transmission Electron Microscopy
The authors thank J. Gao for the Cr/Au electrode deposition and acknowledge helpful discussions with N. V. Smith, F. Marsiglio and A. Slepkov, and financial support from NSERC, CIPI, and iCORE.