Exciton-photon interaction in group III-nitride nanostructures

Abstract

Control and optimization of interaction between light and emitter is a crucial issue for cavity quantum electrodynamics studies and implementation of novel optical devices. Coupling strength between light and emitter is governed by oscillator strength of emitter and local electric field intensity at the position of emitter. The local electric filed intensity can be modified by incorporating emitter in high quality factor and small mode volume cavities such as photonic crystal cavities, micro-disk resonators, and photonic wire. Here, we investigated tailoring photon-exciton interaction in group III-nitride materials using nano- and micro-cavity system. Group III-nitride materials have large oscillator strength due to the large exciton binding energy. However, constructing high quality nitride based micro-cavity using both top-down and bottom-up approaches is very challengeable owing to the mismatch of lattice constant, low refractive index contrast between distributed Bragg reflector materials and high mechanical and chemical stability of nitride materials. To overcome these limitations, crystal geometry is utilized to get a self-aligned or self-assembled cavity structure. De-pending on the coupling strength and loss rate of photons in cavity, weak or strong coupling regime is determined. In the weak coupling regime, we demonstrated deterministic coupling between three-dimensionally nanofocused plasmonic modes and single quantum dot. By depositing a thin silver layer on a site-controlled pyramid quantum dot wafer, three-dimensional plasmonic nanofocusing on each quantum dot at the pyramid apex is geometrically achieved through the silver-coated pyramid facets. Spatial precision is better than any nanopositioning techniques. Enhancement of the quantum dot spontaneous emission rate as high as $22\pm 16$ is measured for all processed quantum dots emitting over ~ 150 meV spectral range. Single photon emission property is measured using second-correlation function and single quantum dot emission is determined at ~200 K. This simple and reliable approach eliminates the major obstacles in the implementation of practical solid-state quantum emitters. In the strong coupling regime, we proposed a novel type of polariton system resulting from strong coupling between two-dimensional exciton and whispering gallery mode photon using core-shell GaN/InGaN hex-agonal microwire. High quality non-polar InGaN multiple-quantum wells were conformally formed on GaN core microwire, which highly suppress quantum confined Stark effect and increase oscillator strength of exciton. Moreover, spatial distribution of multiple-quantum well is well matched with whispering gallery modes inside microwire. Both high longitudinal-transverse splitting of non-polar QWs and high spatial overlap with whispering gallery modes leads to unprecedented large Rabi splitting energy of ~240 meV which is confirmed by angle-resolved and position dependent micro-photoluminescence measurement. This structure provides robust polariton effect with a small footprint, thus it could be utilized for a wide range of interesting applications.