Anisotropic absorption enhancement in hybrid black phosphorous-plasmonic nanograting systems

Although black phosphorous (BP) is a promising two-dimensional material for next-generation infrared (IR) photodetectors, enhancing its quantum efficiency remains challenging. We propose a hybrid BP/plasmonic nanograting with a narrow width and a high-depth groove system to address this challenge. The absorption properties of BP formed on plasmonic nanograting systems with two configurations, namely, an armchair edge normal and parallel to the groove direction, were numerically investigated. These systems demonstrated polarization-selective, wide-angle, near-unity absorption in the IR-wavelength region, and the absorption wavelength was controlled primarily by the groove depth. The BP induced a blue shift of the absorption wavelength, and the wavelength shift was larger for the armchair edge that was normal to the groove direction than that parallel to the groove direction. These results can be attributed to the coupling between the anisotropic surface plasmon resonances of BP and the plasmonic nanogratings. Moreover, this wavelength shift was enhanced by an increase in the carrier density of BP. The BP carrier density can be controlled by its electrical gating. This implies that the detection wavelength can be controlled by electrical gating of the BP. These systems can contribute to the development of high-performance BP-based polarization-selective and/or wavelength-tunable advanced IR photodetectors.