Zno Whispering Gallery Microcavity Exciton Polaritons Dispersion, Experimental Study Of The Lasing And Cohesion

Macroscopic spontaneous coherence of exciton-polariton in semiconductor microcavities has been one of the most exciting fields in condensed matter physics. The experimental realization of coherent condensation of exciton-polariton at high temperature(～K or even up to room temperature) is highly desirable,and the related device application has been attracting much attention in recent years.Ⅱ-Ⅳsemiconductors with large exciton binding energies are promising materials for exciton-polariton studies at elevated temperatures.However,the fabrication of high quality planar cavities on these materials remains challenging so far,though it is crucial for developing polariton devices for room temperature operation.In this thesis, we studies the dispersion,lasing and condensation of exciton-polariton in ZnO nanorod with a hexagonal cross-section which acts as a whispering gallery microcavity(WGM) at room temperature.In the first part of our work,we study the optical properities of exciton-polariton in the linear regime,where the density of exciton-polariton is low and the polariton-polariton interation is weak or even can be neglected.We report for the first time the photoluminescence study of exciton-polariton in ZnO whispering gallery microcavities at room temperature.The details are as follows:(1) We present the direct observation of anticrossing behavior of photon-exciton strong coupling and give a comprehensive dispersion(E=E(k_?)) in a tapered ZnO whispering gallery microcavity by using the micro-confocal photoluminescence spectroscopy.(2) Thanks to the angular resolved spectroscopy,we demonstrate the one-dimensional dispersion of exciton-polariton along the c-axis(E=E(k_//)).(3) The theoretical calculation, based on the coupling oscillators'model and the plane wave model for WGM fits well with the experimental dispersion of exciton-polariton.In the second part of our work,we study the spontaneous coherence of exciton-polariton in the nonlinear regime,where the density of exciton-polariton is high and the polariton-polariton interaction is strong.In this part,we realize the first tunable exciton-polariton lasing in a tapered ZnO WGM at room temperature.By scanning the excitation along the tapered ZnO nanorod,the threshold of polariton lasing and a corresponding blueshift effect as functions of the detuning between the cavity mode and exciton are well investigated.The massive occupation of ground state above the pump power threshold is shown using the angular resolved spectroscopy,which confirms the origin of polariton lasing behavior.The angular distribution of the photoluminescence along the edge of the cross-section(i.e.the plane perpendicular to the c-axis) is also measured;the well-defined emission pattern observed above the power threshold demonstrates the build-up of the coherent exciton-polariton condensate.Furthermore,we present the temperature dependence of exciton-polariton condensation.Basing on the analysis taking into account the temperature effect of bandgap shifting and thus the detuning shifting,we suggest that the LO phonon coupling with exciton-polariton is one of the dominant driving forces for the realization of the exciton-polariton condensation.