Electrical-gain-assisted circularly polarized photodetection based on chiral plasmonic metamaterials

Circularly polarized light (CPL) detectors based on chiral organic materials or inorganic structures hold great potential for highly integrated on-chip applications; however, these devices usually have to seek an optimal balance among the asymmetry factor (g), responsivity (R), and stability. Here, we aim to break such a limitation by combining chiral inorganic plasmonic metamaterials with electrical gain, by which one can enhance both g and R while simultaneously securing the stability. We demonstrate a CPL detector based on "S"-shaped chiral Ag nanowires/InAs/Si heterostructures, where the meticulous construction of the "S"-shaped chiral Ag nanowires with the overlaying InAs channel enables a substantial absorption asymmetry in InAs due to differentiated localized surface plasmon resonances excited by left- and right-circularly polarized (LCP and RCP) light. The InAs serves as a conductive channel, achieving significant electrical gain through photoconductive effects assisted by photogating, gate modulation, and trap effects. The proposed inorganic stable device exhibits a high electrical g of ~1.56, an ultra-high R of ~33,900 A W^-1, a large specific detectivity of ~1.8 × 10¹¹ Jones, and an ultra-short response time of ~23 ns, with the high performance achieved in a broad spectral range from 2 μm to 2.8 μm. Ultimately, by encoding ASCII code 1 and 0 onto LCP and RCP light, respectively, and leveraging the device's heightened discrimination and response performance to these polarizations, we demonstrate a simple yet key-free optical encryption communication scheme at the device level, highlighting its extensive potential for system-level applications.