This paper proposes a kind of high coupling efficiency dual-color quantum well infrared photodetectors (QWIPs) based on dual micro-cavities. By stacking two metal-insulator-metal (MIM) micro-cavities with multiple quantum wells operating at 12.4μm and 15.3μm respectively, the photodetectors can achieve dual-color detection in the long and very long infrared wavelengths. The MIM micro-cavity can excite micro-cavity modes and surface plasmon (SP) modes. By controlling the inner and outer radii of the upper micro-cavity's metallic ring and the side length of the lower micro-cavity's square metallic plate, the operation wavelengths of the two micro-cavities can be independently regulated to match the inherent wavelengths of the dual-color quantum wells. Based on the combined effects of micro-cavity modes and SP modes, the coupling efficiency of the device at peak response wavelengths can hit 587% and 4558%, respectively. In addition, the total absorptions reach 0.76 and 0.9. Compared with the traditional coupling structure, the design of dual micro-cavities QWIPs has a more significant enhancement, which will provide a potential scheme to fabricate high-performance dual-color QWIPs.
Traditional circular polarization detectors use natural chiral materials to distinguish circularly polarized light, but they have relatively low circular polarization extinction ratio (CPER) and light responsivity. This can be effectively improved by integrating chiral materials with detection materials. Common quantum well infrared photodetectors (QWIP) lack the ability to distinguish circularly polarized light. This paper proposes a QWIP that operates in the very long infrared wavelengths, which combines etched GaAs two-dimensional chiral metamaterials with quantum well materials, and achieves a high CPER of 42. Based on the combined effect of surface plasmon polariton (SPP) wave and waveguide resonance, the inter-subband absorption can reach 0.5 when the device is vertically illuminated with 14.2 μm right-handed circularly polarized (RCP) light, which is 15 times higher than that of the standard 45° inclined plane coupling device. At this point, the device has a high coupling efficiency of 810% . When left-handed circularly polarized (LCP) light is incident, the device cannot effectively excite the waveguide resonance effect due to destructive interference. The inter-subband absorption and the responsivity under LCP light are both lower than that of the standard device. This device can enhance RCP light and weaken LCP light, while maintaining high performance of the detector and having the ability to distinguish circularly polarized light. Compared to two-dimensional chiral metamaterials made of metal, our device using etched GaAs is simpler in the manufacturing process, cost-effective, and has a higher CPER. This device can be used for detecting greenhouse gases and thermal imaging in the 14-16 μm infrared wavelength range.
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