Study On The Exciton Photon Coupling In Perovskite Based Semiconductor Microcavity At Room Temperature

Exciton is a kind of quasiparticles in semiconductors when electrons transition from the valence band to the conduction band after the excitation of the photons.While the electrons do not reach the conduction band because they have no enough energy.They are at a certain energy level in the forbidden band and formed a system with a hole in a valence band by Coulomb force interaction.The exciton effect is a strong interaction between the exciton and the external photon,resulting in a nonlinear effect.The exciton-polaritons formed by excitons and photons have attracted much attention because of their unique properties.At present,the study of semiconductor exciton effect is mainly carried out under the conditions of low temperature.Because most of the semiconductor exciton binding energy is too low to the exciton will break down due to thermal motion at room temperature.This limits to the applications of exciton effect.In this thesis,we mainly study the characteristics of the exciton-polaritons in the microcavity at room temperature.The main research object is the exciton-polaritons and emphasizes that the exciton effects of new materials are excited at room temperature.The structure of the microcavity exciton-polaritons is thin hybrid perovskite film sandwiched by Distributed Bragg Reflectors(DBR).Since the transmission characteristic of DBR is have very high reflectivity for a certain wavelength range of light,we often use it to form a semiconductor microcavity to limit the square.Because of the localization of the light field,the excitons in the perovskite and the photons in the semiconductor microcavities will interact strongly,and the spectra will change accordingly.We observed the phenomenon of exciton effect by spectral measurement.In this thesis,the design of DBR using the principle of transmission matrix in the MATLAB software for numerical simulation.In the design,the DBR structure with ultrahigh reflectivity in the wavelength we desired through adjusting the materials with different refractive index,the number of material cycles and the thickness of each layer.In this thesis,according to the design of the DBR structure,we use the electron beam deposition process to prepare a DBR device,and verify the correctness of the design through the reflection spectrum measurement.As the perovskite material has self-assembly properties,homogeneous compact perovskite film in the experiment is difficult to prepare.In this thesis,we proposed to blend polyoxyethylene oxide(PEO)and perovskite in a certain proportion.The mixed solution is processed by spin coating,annealing and other materials preparation process,and then a homogeneous compact perovskite thin film is obtained.In this paper,the microcavity exciton-polaritons is fabricated by electron-beam evaporation,but the preparation process of the upper-layer DBR is difficult,because the perovskite thin film can be damaged by high temperature.We proposed the method of instead of DBR with aluminum,and then prepared out successfully.In this thesis,we measured the perovskite absorption spectrum to verify the existence of excitons in perovskite thin films at room temperature,and measured the exciton effect in the microcavities exciton-polaritons by the measurement of angular resolution spectra.In this thesis,we have observed the inverse crossover in the spectrum at room temperature,which means that there is strong coupling in the microcavity exciton-polaritons,it means the exciton effect is exists at room temperature.