Room-temperature polariton luminescence from a bulk GaN microcavity

We report strong exciton-photon coupling at room temperature in a hybrid high quality bulk $3\lambda ∕2$ GaN cavity with a bottom lattice-matched $\mathrm{Al}\mathrm{In}\mathrm{N}∕\mathrm{Al}\mathrm{Ga}\mathrm{N}$ distributed Bragg reflector through angle-resolved polarized photoluminescence (PL). Coupling of the optically active free excitons ($X_A$, $X_B$, and $X_C$) to the cavity mode is demonstrated, with their contribution to the PL spectra varying with polarization. Under TE polarization, exciton oscillator strengths for $X_A$ and $X_B$ are about one order of magnitude larger than in bulk GaAs. Photoluminescence exhibits a strong bottleneck effect despite its thermal lineshape.

Figure 1

(a) Scanning electron microscope image of the GaN cavity surrounded by an $\mathrm{Al}\mathrm{In}\mathrm{N}∕\mathrm{Al}\mathrm{Ga}\mathrm{N}$ bottom DBR and a $\mathrm{Si}{\mathrm{O}}_2∕{\mathrm{Si}}_3{\mathrm{N}}_4$ top DBR. (b) RT PL spectrum of a relaxed GaN template layer grown on sapphire vs PL spectrum taken on the half-microcavity structure. The topmost spectrum has been upshifted for the sake of clarity.

Figure 2

(a) RT PL spectra as a function of angle for TM polarization. (b) Same as (a), but for TE polarization. Lines are a guide to the eye. The position of excitons is also quoted.

Figure 3

Experimental energy positions vs $\theta$ together with calculated polariton dispersion curves (see text for details). The uncoupled modes are also reported. (b) Relative fractions of each of the uncoupled modes: cavity-photon $C$ (---), $X_A$ (—), $X_B$ (–∙–), and $X_C$ (⋯) in the mixed polariton modes.

Figure 4

Experimental PL spectrum measured at $\theta =16°$ (—) and the corresponding calculated spectrum (– – –). Inset: Experimental polariton population of the LPB (∎) and calculated one considering a thermalized population (– – –).