Time-resolved terahertz spectroscopy is used to probe ultrafast carrier dynamics and terahertz conductivity in photoexcited thin films of silicon nanocrystals, polynanocrystalline silicon, and epitaxial silicon-on-sapphire. We show that a Drude-Smith model provides an excellent fit to the observed transient terahertz conductivity in all of our samples, revealing a transition from a Drude-like response with low carrier backscatter in bulk silicon-on-sapphire to a non-Drude-like, localized behavior with high carrier backscatter in the silicon nanocrystal films. Evidence for long-range conduction between nanocrystals is observed, and we show that the photoconductive lifetime of the silicon nanocrystals is dominated by trapping at $\mathrm{Si}∕\mathrm{Si}{\mathrm{O}}_2$ interface states.

• Received 24 March 2006

DOI:https://doi.org/10.1103/PhysRevB.73.193311