Broadband Infrared-To-Visible Detector Enabled by a Voltage-Gated Metasurface Photocathode with Field-Assisted Electron Multiplication

Overcoming the spectral limitations of conventional photodetection systems that typically operate within narrow bandwidths, this work presents an optoelectronic platform that achieves efficient multiwavelength photon-electron-photon spectral conversion with total energy conversion efficiencies of approximately 11.7% (9.7 μm), 8.2% (2.2 μm), and 4.7% (655 nm), with all inputs collectively translated to a sharp emission centered around 545 nm. The device features a precisely engineered metasurface photocathode that exploits surface plasmon resonance (SPR) to induce localized electron accumulation under low-power optical excitation. Critically, by voltage-gating the cathode bias, the system establishes distinct spectral preference windows, thereby enabling wavelength-selective optimal conversion through simple electrical tuning. This approach permits flexible switching between pure photoexcitation and field emission regimes by adjusting the VMN bias beyond a threshold of ∼281 V. Full vacuum-packaged prototypes reveal photocurrent enhancements exceeding 2 orders of magnitude relative to the dark current (<10 nA) under sub-milliwatt infrared illumination, measured across an operational voltage ensemble of {VMN: 0–400 V, VMCP: 1600 V, VFM: 5900 V}. Collectively, this architecture establishes a versatile voltage-tunable platform for broadband spectral conversion, surpassing traditional single-band intensification approaches and opening avenues for compact infrared night vision, advanced biomedical imaging, and low-cost multispectral sensing.