In this work we study the spatial distribution of photon modes confined in a 0D cavity and a 1D W1 on AlN-based photonic crystal membranes by spectrally resolved confocal microscopy in the ultra-violet spectral range. The analysis of the influence of the fabrication-induced disorder of the PC on the photon modes show that the cavity modes are robust with respect to disorder, whereas the 1D modes of the W1 waveguide are localized near its cut-off frequency. Modifications of the photon local density of states will be compared to simulations of weakly disordered photonic structures.

We present spatially- and time-resolved photoluminescence experiments on polar GaN/AlGaN quantum well structures,showing exciton propagation distance of tens of micrometers from generation position and exciton radiative lifetimes oftens of microseconds. We study in detail the dynamics and range of their relaxation/diffusion along the growth plane, asa function of temperature.

Self-assembled semiconductors QDs are of great interest in fundamental physics as well as inapplied physics. In GaN/AlN heterostructures, the huge band-offset and the strong excitonicbinding lead to an important exciton confinement allowing an emission even at roomtemperature. GaN QDs grown along the (1000) axis are named “polar” due to their stronginternal electic field which lead to the so-called QCSE. The most important modifications due tothis electric field take place in thick QDs emitting around 330nm and more : the luminescence isredshifted and the radiative lifetime is strongly increased [1]. On the other hand, in thin QDs(smaller than 2.3nm), the quantum confinement plays the key role, thus leading to a significantlysmaller homogeneous linewidth and to the resolution of the exciton fine-structure splitting[2]. Concerning the radiative recombination processes, several papers reported measurements at330nm or more either in polar[3] or non-polar[4] nanostructures. Experimental data on excitonicradiative lifetime are also existent in thin QDs but on a limited dynamical range where thepossible influence of QCSE is not discussed [5].In this work, we report time-resolved photoluminescence measurements in GaN/AlN QDsemitting between 280nm and 360nm. For QDs emitting at 300nm we observe a biexponentialdecay dynamics of the photoluminescence signal (Fig.1, left). The fast component (450 ps) isinterpreted as the radiative lifetime of the QDs in the absence of a noticeable redshift of thetransition. Thanks to our better signal-to-noise ratio than in Ref. 5, we are able to extract a slowcomponent (2 ns) which may originate either from feeding from the barrier or other processesinside the QD. Power dependent experiments further confirm this interpretation. We observe thatthe fast component remains the same as a function of excitation power (Fig.1, right) and, moreimportantly, that the intensity ratio keeps the same value. This rules out any contribution fromthe relaxation of multi-carriers complexes such as biexciton or trion in the short time dynamics

ZnO is a wide bandgap semiconductor with strong excitonic properties, in particular a large oscillator strength and a large exciton binding energy. It therefore raises a strong interest for the generation and control of polariton condensates up to room temperature.The realization of planar ZnO microcavities with good quality factors has long been a strong challenge. We first demonstrated in 2011 a ZnO polariton laser operating at zero exciton-photon detuning and a temperature of 120 K [1], based on a hybrid microcavity (AlN/AlGaN DBR, MBE-grown ZnO, SiO2/SiN DBR) with a quality factor Q=450. This value was still too small to allow the observation of polariton lasing up to room temperature. A different approach was implemented based on a ZnO active layer of high crystalline quality, embedded between two dielectric DBR; such a fully-hybrid microcavity exhibits a high quality factor (Q>2000) and a large Rabi splitting (250 meV). We have observed the condensation of polaritons in this bulk ZnO microcavity over an unprecedented range of exciton-photon compositions and of temperatures, up to room temperature [2]. The complete phase diagram of the ZnO polariton laser has been measured, showing that its threshold is only 6 times larger at 300 K than at 8 K. It is in a good qualitative agreement with the simulations of exciton and polariton relaxation in a kinetic model. This tunability represents an important progress compared to our previous demonstration [1], as well as to other recent reports [3]. It also confers a strong advantage to ZnO microcavities compared to GaN [4], since strong excitonic condensates can here be investigated.The cavity with Q>2000 however presents a strong gradient of the cavity thickness hindering the generation of extended condensates. Equivalent cavities without such a gradient have therefore been developed in the last years, based on high quality AlN/AlGaN DBRs on mesas. Our most recent investigations are dedicated to the role of the shape of the exciting laser spot on the condensate generation. Condensate propagation is observed under tightly focused excitation, driven by the interaction with the reservoir as in GaAs microcavities, whereas localization of the polariton condensates is observed for larger excitation areas.