Polarization behavior of the exciton-polariton emission of ZnO-based microresonators
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1208-O18-08
Polarization behavior of the exciton-polariton emission of ZnO-based microresonators Chris Sturm, Helena Hilmer, Rüdiger Schmidt-Grund and Marius Grundmann Universität Leipzig, Institut f. Experimentelle Physik II, Linnéstr. 5, 04103 Leipzig, Germany ABSTRACT We present the polarization behavior of the exciton-polariton luminescence of a ZnObased all-oxide resonator. A splitting in the emission energy between the s- and p-polarized photoluminescence of the lower polariton branch was observed which increases with increasing emission angle. It is caused by the polarization behavior of the uncoupled cavity-photon mode, and reaches a maximum of about 5 meV at an emission angle near the bottleneck region. For larger angles the energy splitting decreases. Additionally to the energy splitting, we observed differences in the photoluminescence intensity which we trace back to different occupation of the lower polariton branch for the two polarizations. Whereas for p-polarization a bottleneck effect is clearly observable, this effect is much weaker for s-polarization. These findings indicate that the relaxation of hot carriers into the bottleneck region is enhanced for the p-polarized photoluminescence compared to the s-polarized one. The differences between these two polarizations are most pronounced for a very large negative detuning and vanish with increasing detuning. INTRODUCTION The photoluminescence of exciton-polaritons has been widely investigated in the last years since it yields information about the exciton-polaritons, e.g. the exciton-photon coupling and the exciton-polariton scattering processes [1 – 7]. The exciton-polaritons are bosonic quasiparticles formed by the coupling between an exciton and a photon, which can be used for the realization of ultra-low threshold laser, optical amplifiers and Bose-Einstein condensation (BEC) even above room temperature [1 – 5]. Of special interest is the formation of exciton-polaritons in ZnO-based resonators since they are stable way above room temperature combined with a large exciton-photon coupling strength [8]. Recently we have shown such a resonator being in the strong coupling regime up to 410 K [9]. However, up to now, BEC in ZnO-based resonators has not been reached which could be caused by an inefficient relaxation of the exciton-polaritons to their ground state. In this work we present the polarization dependence of the exciton-polariton photoluminescence which gives an insight in the relaxation and scattering processes of the exciton-polaritons and therefore provides a step forward to the realization of BEC in such resonators. EXPERIMENTAL The ZnO-based resonator was grown by pulsed laser deposition [9] and consists of a wedge-shaped half wavelength ZnO cavity. This cavity was embedded between two all-oxide Bragg reflectors (BR) made of 10.5 layer pairs of yttria stabilized zirconia (YSZ) and Al2O3. The reflectivity of such BR is typically larger than 99.2% [10, 11]. The exciton-polaritons were investigated by photoluminescence (PL) measurements at
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