A Correlation between the Emission Intensity of Self-Assembled Germanium Islands and the Quality Factor of Silicon Photonic Crystal Nanocavities

TL;DR

This study investigates how the emission intensity of self-assembled germanium islands in silicon photonic crystal nanocavities correlates with the cavity quality factor, revealing that higher quality factors lead to decreased emission due to reabsorption effects.

Contribution

The paper provides experimental and theoretical evidence linking emission intensity decline to reabsorption and free carrier absorption in high-Q silicon photonic nanocavities.

Findings

Emission intensity decreases with increasing quality factor.

Reabsorption of emitted photons causes the observed trend.

Free carrier absorption limits cavity-mediated light enhancement.

Abstract

We present a comparative micro-photoluminescence study of the emission intensity of self-assembled germanium islands coupled to the resonator mode of two-dimensional silicon photonic crystal defect nanocavities. The emission intensity is investigated for cavity modes of L3 and Hexapole cavities with different cavity quality factors. For each of these cavities many nominally identical samples are probed to obtain reliable statistics. As the quality factor increases we observe a clear decrease in the average mode emission intensity recorded under comparable optical pumping conditions. This clear experimentally observed 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 evidence that reabsorption of photons emitted into the cavity mode is responsible for the observed trend. In combination with the observation of cavity linewidth broadening in power dependent measurements, we conclude that free carrier absorption is the limiting effect for the cavity mediated light enhancement under conditions of strong pumping.