Metallic nanocavities have been actively studied for realizing nanolasers with low threshold. Presence of resonance modes with high cavity Q values is the indication of low internal loss that leads to low threshold lasing. However, cavity Q values observed in metallic nanocavities below lasing threshold remain low at present on the order of 100 to 500. We study the possibility to realize higher resonance Q values with a metallic nanocavity. For probing purpose of cavity modes we propose to employ broad mid-gap-state optical emission of n-type GaAs. With this method we report the observation of a resonance mode with the high Q value of 3800 at room temperature with the metallic nanocavity. The cavity mode is identified as a whispering-gallery mode with finite-element- method simulation

Metallic cavities have been extensively studied to realize small-volume nanocavities and nanolasers. However cavity-resonance quality (Q) factors of nanolasers observed up to now remain low (up to ~500) due to metal optical absorption. In this paper, we report the observation of highest Q factors of 9000 at low temperature and ~6000 near room temperature in a metallic cavity with a probe of sub-bandgap emission of Si-doped GaAs. We analyze the temperature dependence of cavity-mode resonance wavelengths and show that the refractive-index term dominates the measured temperature dependence. We also show that this refractive-index term is cavity-mode dependent and the fitting procedure offers a new method to identify cavity modes. We simulate the metallic cavity with finite-element method and attribute the high-Q cavity mode to a whispering gallery optical mode. This mode is shown to have isotropic polarization dependence of the output emission, which is preferable for quantum information applications.2