Light amplification in silicon nanocrystals by pump and probe transmission measurements

Net optical gain in silicon nanocrystals (Si-nc) has been measured by pump and probe transmission experiments. Si-nc active layers have been produced by plasma enhanced chemical vapor deposition on transparent quartz substrates. Continuous and pulsed pump and probe transmission measurements have shown clear evidences of net probe amplification with fast (nanosecond) response time. Transfer matrix and rate equations modeling of the nonlinear signal transmission allowed to extract the gain spectra for different pump intensities yielding good qualitative agreement with the experimental data. Gain cross sections per nanocrystals of the order of 3×10−16cm2 have been deduced. The physical origin of the optical amplification is interpreted within a four level recombination model describing the dynamics of strongly localized excitons at the Si-nc∕SiO2 interface.