Enhanced photoluminescence from germanium-based ring resonators

We report the enhancement of direct bandgap emission from germanium ring resonators based on silicon-on-insulator (SOI). As a consequence of their strong confinement, a record quality factor $\left(Q\right)$ of 620 is obtained that is an order of magnitude higher than that previously characterized for crystalline germanium microcavities. We also describe a pump power dependency of $Q$ due to bandedge shifts not previously reported for silicon-or germanium-based emitters. A decline in the relative peak to baseline intensities with lower $Q\mathrm{s}$ is attributed to the Purcell effect on account of the wavelength-scale dimensions and high index contrast of our samples.