Continuous wave spectroscopy of nonlinear dynamics of Si nanocrystals in a microdisk resonator

摘要

We report on a study of the recombination dynamics of silicon nanocrystals (Si-ncs) embedded in a planar whispering-gallery mode resonator. Fundamental properties of exciton dynamics in Si-ncs, in particular their absorption cross-section and excited carrier-related losses, can be extracted from continuous-wave spectroscopy by analyzing the resonance linewidths at different excitation powers. Observation of nonlinear drifts of mode peak positions in the same experiment allows us to model the nonlinear refractive index of the nanocrystalline material. The theoretical results confirm that the observed sublinear blue and linear redshifts of resonance peak positions are induced by excited carrier effects and thermal heating at low and high pump powers, respectively. The extracted thermo-optic coefficient, k_T = 1.46 × 10~(-4) K~(-1), and excited carrier refraction, K_(ec) = —107 × 10~(-23) cm~3, in Si-ncs, are of relevance since they may induce important modulation of the fine modal structure of an optically active cavity.