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.

We report the observation of midinfrared intersubband (ISB) absorption in nearly lattice-matched $\mathrm{Al}\mathrm{In}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ multiple-quantum-wells. A clear absorption peak is observed around $3\mu \mathrm{m}$ involving transitions from the conduction band ground state to the first excited state. In addition to ISB absorption, photoluminescence experiments were carried out on lattice- matched $\mathrm{Al}\mathrm{InN}∕\mathrm{GaN}$ single quantum wells in order to determine the spontaneous polarization discontinuity between GaN and ${\mathrm{Al}}_{0.82}{\mathrm{In}}_{0.18}\mathrm{N}$ compounds. The experimental value is in good agreement with theoretical predictions. Our results demonstrate that the $\mathrm{Al}\mathrm{In}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ system is very promising to achieve crack-free and low dislocation density structures dedicated to intersubband devices in the $2–4\mu \mathrm{m}$ wavelength range.

The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of $\mathrm{In}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found $(Q>4000)$ . Laser action at $\sim 420\mathrm{nm}$ is achieved under pulsed excitation at room temperature for a peak power density of $400\mathrm{kW}∕{\mathrm{cm}}^2$ . The lasing emission linewidth is down to $0.033\mathrm{nm}$ .

In situ XRD and IR optical measurements demonstrate the coexistence of M₁ and R phases during the SMT transition of VO₂ thin films.