The spatial distribution of photon modes confined in a 0D cavity and a 1D W1 waveguide is investigated on AlN-based photonic crystal (PC) membranes by spectrally resolved scanning confocal microscopy in the ultra-violet spectral range. The influence of the fabrication-induced disorder of the PC on the photon modes is analyzed. The cavity modes are shown to be robust with respect to disorder, whereas the 1D modes of the W1 waveguide are localized near its cut-off frequency. Those modifications of the lowest energy photonic modes are compared to simulations of weakly disordered photonic structures.

A ZnO planar optical microcavity displaying room-temperature polariton lasing has been fabricated. The cavity combines optimum crystalline quality, as given by the ZnO bulk single-crystal substrate employed as active region, and optimum photonic quality, as obtained by the use of two dielectric SiO2/HfO2 Bragg mirrors. A maximum cavity quality factor of about 3000 has been measured, enabling the observation of room-temperature polariton lasing in a wide range of cavity-exciton detuning conditions. Typically, the polariton lasing transition is accompanied by an increase of the output intensity by more than two orders of magnitude, a reduction of the emission linewidth by a factor 5 and a relatively small blueshift of the lower polariton branch (less than 5% of the Rabi splitting).

We report exciton-polariton condensation in a new family of fully hybrid ZnO based microcavity demonstrating the best-quality ZnO material available (a bulk substrate), a large quality factor (~4000) and large Rabi splittings (~240 meV). Condensation is achieved between 4 and 300 K and for excitonic fractions ranging between 17% and 96 %, which corresponds to a tuning of the exciton-polariton mass, lifetime and interaction constant by one order of magnitude. We demonstrate mode switching between polariton branches allowing, just by controlling the pumping power, to tune the photonic fraction by a factor 4.

Phonon-assisted exciton formation in ZnO/(Zn, Mg)O single quantum wells grown on C-plane oriented substrates.

In this work, we study the spectroscopy of two types of nanocavities. The first one consists of Al(Ga)N microdisk resonators embedding GaN QDs. We have observed and modelled their optical modes, called whispering gallery modes, with promising quality factors from 1000 to 7000 (Optics Letters, vol. 36 p.2203 - 2011). The second type of nanocavities is photonic crystals obtained by small modifications of a W1 waveguide in an AlN photonic crystal membrane containing QDs. The room temperature photoluminescence of the embedded quantum dots reveals the existence of even-symmetry and odd-symmetry confined cavity modes and guided modes. Cavity mode quality factors up to 4400 at 395nm and 2300 at 358nm are obtained (APL, 100 p.191104 - 2012). These results will be compared to state of the art nitride microdisks and photonic crystal cavities.

Time-resolved photuminescence spectroscopy investigations of nonpolar homoepitaxial ZnO/(Zn,Mg)O quantum wells.

Semiconductor-based microcavities appear as a prolific system for studying light-matter interaction between a spatially-confined photonic mode and an excitonic resonance. The quasiparticles arising from this coupling (microcavity-polaritons) have enabled in the last years the observation of new lasing regimes as well as polariton Bose-Einstein condensates, vortices and lately solitons. In this panorama ZnO appears as an alternative material to more mature ones, such as GaAs or CdTe, with larger oscillator strengths and enhanced exciton stability. These two properties render ZnO very interesting for studies and applications where large particle densities and/or high temperatures are required. However, the fabrication of ZnO-based microcavities is still challenging and it often requires the use of either nitrides or dielectric materials for the DBRs. Indeed, polariton lasing was demonstrated for the first time in a ZnO-based microcavity only in 2011 [1]. In this work we report on the optical study of a fully-hybrid ZnO-based microcavity in which we combine a high quality active region made up of bulk ZnO and a high cavity quality factor, thanks to the use of two dielectric DBRs. With the cavity Q-factor measured to be more than 1500, polariton lasing is clearly observed from low to room temperature, characterized by a strong linewidth reduction, a small blueshift compared to the Rabi splitting, and an increased emission intensity (three orders of magnitude increase). Furthermore, the wedged-shape of the ZnO active region allows accessing a large range of detunings between the exciton and cavity modes. Under these conditions, the polariton lasing regime has been systematically studied as a function of temperature and detuning, from low to room-temperature. The detailed phase diagram demonstrates the important role played by LO-phonons in the dynamics of the polariton relaxation in ZnO [2], evidenced by a local threshold minimum as a function of detuning. The different relaxation regimes, i.e. kinetic Vs thermodynamic, are further investigated by analyzing a thick cavity region where several lower polartion branches (LPBs), with very different excitonic/photonic fractions are observed. Condensation is observed to take place on the optimum branch as determined by the actual detuning and excitation power. These observations are promising for realizing future multi-mode tunable lasers and room temperature optical switches. References [1] T. Guillet et al., Polariton lasing in a hybrid bulk ZnO microcavity, Appl. Phys. Lett. 99 161104, 2011. [2] L. Orosz et al., LO-phonon-assited polariton lasing in a ZnO-based microcaivty, Phys. Rev. B, 85, 121201(R), 2012.