From strong to weak coupling regime in a single GaN microwire up to room temperature

Large-bandgap semiconductor microwires constitute an advantageous alternative to planar microcavities in the context of the room temperature strong coupling regime between excitons and light. In this work, we demonstrate that in the undoped half of a single GaN microwire, the strong coupling regime is achieved up to room temperature with a large Rabi splitting of 115 meV. The demonstration relies on a method that does not require any knowledge a priori of the energy of the uncoupled whispering gallery modes in the microwire, i.e. the details of the microwire cross-section shape. The other half of the microwire is heavily n-doped. Thus, within the same microwire, the exciton oscillator strength transits from its nominal value to zero within a region of 2 μm length. Using this property, we can observe the dispersion properties of a given whispering gallery mode in both the strong and weak coupling regimes.