Associate professor, Department of Chemistry and Applied Chemistry, Saga University, Japan

Speech Title: Lead Halide-Based Layered Perovskite Films Applicable to Cavity Polariton Devices
Abstract: In recent two decades, the semiconductor microcavities, which are consisting of distributed Bragg reflectors (DBRs) and semiconductor quantum-wells, have much attractive attention in both fundamental physics and practical applications. Light-matter interactions in the microcavities modify the exciton emission from quantum-wells in the two regimes; weak coupling and strong coupling. In the strong coupling regime, the excitons and confined photons cannot be assumed independent eigenstates in the cavity. Mixing of the eigenstates in the strong coupling regime forms new eigenstates, namely, cavity polaritons which are half-light, half-matter bosonic quasi-particles. It is demonstrated theoretically and experimentally that they exhibit new phenomena based on the bosonic natures. Through the phenomena, the cavity polaritons are expected to realize new optoelectronic devices (cavity polariton devices) such as polariton laser, high speed optical switches, spin-memory and so on.
The studies on the micorcavities have been conducted mainly in compound semiconductors, for example, II-VI, III-V semiconductors. To construct the cavities using the compound semiconductors, one need to employ a highly sophisticated preparation procedure, molecular beam epitaxy (MBE). In the procedure, quantum-well structures are prepared by using the epitaxial growth of semiconductor layers at mono-atomic level under an extremely high vacuum condition. Therefore, the preparation facilities and cost are very high. Lead halide-based layered perovskites, which are described by the following formulae, [(RNH3)2PbX4, RNH3; organic ammonium cation, and X; halogen], self-organize a quantum well structure, where an inorganic semiconductor layer of two-dimensionally corner-sharing octahedral PbX6 and a dielectric organic layer of RNH3 are alternately piled up. A large dielectric confinement of excitons in the inorganic semiconductor layer derives formation of a stable exciton with a large binding energy of several hundred meV and a large oscillator strength.) Owing to the stable excitons, they exhibit efficient photoluminescence, electroluminescence, and optical nonlinearities.
In addition to their attractive exciton properties, their self-organizing nature gives us easy ways, which are antithetical to MBE, to construct quantum-wells. We can prepare the well-defined multi-quantum-well structure, which have no lattice mismatch, at ambient condition by using simple techniques, e.g. spin-coating, dipping, dual vapor deposition and so on. The features encourage us to employ the lead halide-based layered perovskites as a quantum-well material for the cavity polariton devices.
In this presentation, preparation techniques to construct cavity polariton devices using the layered perovskites and optical properties of the layered perovskite are reported.