The Dispersion And Energy States Tailoring Of Exciton-polaritons In Single And Hybrid Microcavities

Exciton-polaritons are essentially quantum oscillation states formed via the strong coupling between semiconductor excitons and cavity photons.Such quantum oscillation states can be regarded as elementary excitations or quasi-particles.Compared with other microscopic particles,exciton-polaritons are famous for their intrinsic half-light half-matter nature.Thanks to their inherited excitonic component,exciton-polaritons can interact with other charge carriers via Coulomb forces.Their inherited photonic component,on the other hand,gives them an extremely small effective mass(typically on the order of 10^-5 m_e).As a result of this unique half-light half-matter nature,exciton-polaritons are ideal testing beds for the study of macroscopic quantum phenomena.Lots of interesting physics have been reported in the past decades based on exciton-polaritons,such as Bose-Einstein condensation at room temperature,superfluidity and vortex.Prior to the commercial application of exciton-polaritons,the development of an efficient way to tailor their energy states is essentially important.Towards this aim,the introduction of optical microcavities has been proven to be one of the most efficient strategies.Indeed,studies show that microcavities are not only important for the formation of exciton-polaritons,but also highly efficient to engineer their electronic and optical properties.In this work,we followed this idea to engineer the energy states and optical properties of exciton-polaritons via the introduction of hybrid microcavities.Based on our home-built angle-resolved micro-PL system,we also performed experimental studies on the dynamics of exciton-polaritons in hybrid microcavities.The studies in this thesis are summarized in the following:（1）Experimental studies on the fine structures of exciton-polaritons in one-dimensional ZnO whispering gallery microcavity.In ZnO,there exist three types of excitons,i.e.A-exciton,B-exciton and C-exciton.Theoretically,all these three types of excitons can couple strongly with light fields to form exciton-polaritons.However,little attention has been paid to such fine structures of exciton-polaritons so far.In this work,we grew high quality ZnO microrods via chemical vapor deposition and performed systematic studies on the dispersion relation of exciton-polaritons using our home-built angle-resolved micro-PL system.Interestingly,we observed three sets of polariton dispersions in our one-dimensional ZnO microcavities.With the help of theoretical calculations using the coupled oscillator model,we verified that the three sets of dispersion are exactly polariton branches corresponding to A-exciton,B-exciton and C-exciton,respectively.To the best of our knowledge,this is the first observation of polariton fine structures in ZnO.（2）Studies on engineering the energy states of exciton-polaritons via hybrid microcavity.Efficient control of the energy states of exciton-polaritons is key to their commercial application in optoelectronics.In this work,we tried to tailor the dispersion relation and optical properties of exciton-polaritons using a hybrid whispering gallery and Fabry-Perot microcavity.The Fabry-Perot microcavity is formed by placing a ZnO microrod above the Si substrate and elaborately adjusting the distance between them.By means of angle-resolved micro-PL studies,we found that the dispersion relation of exciton-polaritons can be engineered conveniently by controlling the distance between ZnO microrod and Si substrate.Combined with theoretical fittings using the coupled oscillator model,we confirmed that the engineered dispersion relation of exciton-polaritons is due to the coupling between the whispering gallery and Fabry-Perot microcavities.These results demonstrate the feasibility of engineering the energy states of exciton-polaritons using hybrid microcavities.（3）Dynamics of exciton-polaritons at high excitation power.In this work,we inject both exciton-polaritons and hot excitons into ZnO microrods through non-resonant optical pumping.Due to the limited lifetime of the exciton reservoir and the repulsive interaction between polaritons and excitons,our angle-resolved micro-PL measurements reveal rich physics related to the dynamics of exciton-polaritons.These observations are well rationalized by taking into account the propagation of exciton-polaritons in real space and the relaxation of the excitonic reservoirs.