| In recent years, the strong coupling of interaction between microcavities and intersubband transitions has caused tremendous research interest, fertile both for fundamental and applied research. The coupling strength of systems can be strongly enhanced by embedding the doped quantum wells into various optical microcavities, one of which is plasmonic microcavity. A major advantage of plasmonic microcavity is that it allows the observation of strong coupling phenomenon under normal incidence, whereas in traditional microcavities the experiments are performed only at almost gazing incidence and the light was confined by total internal reflection. Moreover, the plasmonic cavities often exhibit high coupling efficiency ard a strong field enhancement in the near-field. In this paper, we design a metal-insulator-metal (MIM) structure plasmonic cavity, which consists of a perforated metal film, a bottom continuous Au film, and a semiconductor dielectric spacer. On this basis, we study the strong coupling regime of plasmonic microcavity and intersubband transitions, and the plasmonic microcavity is applied in quantum well infrared photodetectors(QWIP).(1) We simulate the microcavity structures with Finite Diffence Time Domain(FDTD). We discover that the lowest-order resonance f1 is the hybridized mode of propagating surface plasmon(PSP) and localized surface plasmon(LSP). For a given f1,we can realize the mode transformation between PSP mode and LSP mode through changing cross hole structure, which is a new freedom for modulating the interaction of light and matter. What’s more, there is large field enhancement and high ratio of polarization conversion.(2) The plasmonic microcavity embedded with multiple quantum wells is studied with the permittivity of quantum well layer regarded as a Lorenzian model. When the lowest-order resonance f1 and the intersubband transitions become similar or equal, the two systems couple and Rabi splitting happens. The ratio between the vacuum Rabi frequency and the bare system excitation frequency can be applied to access the strength of interaction. Then, we study the coupling of different plasmonic modes and quantum wells with a given f1. With the cavity mode transforming from LSP mode to PSP mode, the strength of interaction increases from 20.75%to 25.75%, which is mainly dominated by the polarization conversion ratio (E2/x)/(E2) of plasmonic modes.(3) By studying the electric field enhancement and electric field distribution of f1= 20THz and f2=30THz of this cavity, we find the cavity is particular suitable for designing a new plasmonic two color QWIPs. Experimentally, we firstly measure the quantum well response of the wafer. The quantum wells corresponding to f2= 30THz is worse and hardly is used to infrared detection. Secondly, we explore the fabrication process of our devices. The overall process proceeds as follows: electron-beam evaporation Ti/Au deposition, Au-Au wafer bonding, mechanical polishing, selective etching of GaAs, selective etching of etch-stop layer, photolithography, EBL and Au-wire bonding. Finally, current-voltage (Ⅰ-Ⅴ) curve measurement is taken for room temperatures with a Schottky contact-0.5V, and photoresponse of QWIPs is measurement with FTIR with a desired result agreeing well with simulation.Our study shows that the system of plasmoic microcavity and quantum wells is a powerful tool to investigate cavity electrodynamics and the plasmonic microcavity can be applied in other optoelectronic devices. |
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