Polariton condensates in ZnO microcavities: generation, dynamics and localization

Thierry Guillet (1) , Rereao Hahe (1) , Olfa Kamoun (1) , Christelle Brimont (1) , Pierre Valvin (1) , Sihem Jaziri (2) , Dimitri Solnyshkov (3) , Guillaume Malpuech (3) , Sophie Bouchoule (4) , Xavier Lafosse (4) , Gilles Patriarche (4) , Feng Li (5) , Mathieu Leroux (5) , M.J. Rashid (5) , Fabrice Semond (5) , Jesús Zúñiga-Pérez (5)

1 L2C - Laboratoire Charles Coulomb
2 Faculté des Sciences de Bizerte [Université de Carthage]
3 IP - Institut Pascal
4 LPN - Laboratoire de photonique et de nanostructures
5 CRHEA - Centre de recherche sur l'hétéroepitaxie et ses applications

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.

Domaines: Autre [cond-mat.other]

Thierry Guillet, Rereao Hahe, Olfa Kamoun, Christelle Brimont, Pierre Valvin, et al.. Polariton condensates in ZnO microcavities: generation, dynamics and localization. 15th International Conference on Light-Matter Coupling in nanostructures, Jun 2014, Montpellier, France. ⟨hal-01132088⟩