Broadband MWIR meta-absorbers using hybridized ENZ-plasmonic modes

Mid-wave Infrared (MWIR) detectors based on Indium Antimonide (InSb) and Mercury Cadmium Telluride (MCT) are useful for a range of applications in autonomous systems, industrial and environmental monitoring, and night vision for security and defence. Their requirement for cryogenic cooling, however, limits their applications, decreasing their portability, increasing power consumption, and slowing down startup times. InSb detectors operated at room temperature would be more portable, consume less power, and speed up startup times. However, their limited sensitivity, high noise, and longer response times make them unsuitable for high-end applications. Plasmonic metasurfaces have been widely deployed for optical absorption enhancement, but they have a narrowband response. In this work, we present a numerical study that investigates the feasibility of using transparent conducting oxide (TCO) as the epsilon-near-zero (ENZ) layer surmounted by a gold plasmonic metasurface as the top electrode. This Metal-Semiconductor-Metal Schottky devices based on InSb shows near-unity broadband absorption of incident MWIR light. The synergy between ENZ layer and the designed plasmonic metasurface allows for a homogeneous broadband absorption in the underlying InSb layer, insensitive to the polarisation and angle of incident light. The thickness of the TCO layer, carrier density, and the parameters of the plasmonic metasurface are optimised to produce high absorption (>90%) in the wavelength span 3.37–4.55 μm, corresponding to a high atmospheric transmission channel. The inclusion of a TCO layer enhances the optical performance while also providing an electrical path for the photo-generated current. The ENZ-enabled plasmonic meta-absorber device that we propose has therefore the potential to achieve higher detectivity, paving the way for the development of nextgeneration miniaturized, high-speed, uncooled MWIR focal plane arrays (FPAs).