Ultrafast carrier dynamics and carrier localization in thermally annealed Si nanoclusters

We present results of time-resolved terahertz pulse spectroscopy experiments on thermally deposited and annealed Si nanoclusters embedded in a SiO$_{2}$ matrix. These clusters range in size but are on the order of 5 nm in diameter, which is comparable to the Bohr radius in Si where carriers are expected to be strongly localized. The frequency-resolved conductivity of these samples after excitation by a 400 nm, 100 fs pump pulse is non-Drude like with a real component that increases with frequency and a negative imaginary component indicative of carrier localization. A series of samples is investigated as a function of anneal temperature, showing transient absorption decays ranging from a few picoseconds to several hundred picoseconds as the anneal temperature increases. Several models to explain the observed response are discussed. The authors acknowledge financial support from NSERC, CIPI and iCORE.