Correlation between emission intensity of self-assembled germanium islands and quality factor of silicon photonic crystal nanocavities

We present a comparative microphotoluminescence study of the emission intensity of self-assembled germanium islands coupled to the resonator mode of two-dimensional silicon photonic crystal defect nanocavities. The cavity-mode intensity is investigated for L3 and hexapole cavities with a range of different mode quality factors. For each type of cavity, many nominally identical samples are probed to obtain reliable statistics. As the cavity-mode quality factor increases, we observe a clear reduction of the average mode emission intensity under conditions of strong optical pumping. This clear trend is compared with simulations based on a dissipative master-equation approach that describes a cavity weakly coupled to an ensemble of emitters. We obtain direct evidence that reabsorption of photons in the cavity is responsible for the observed trend. When combined with the observation of cavity linewidth broadening in power-dependent measurements, we conclude that free carrier absorption limits the cavity-mediated light enhancement under conditions of strong excitation.