Domain‐Engineered Metasurfaces for Monolithic Photodetection in Lithium Niobate

ABSTRACT The development of multifunctional ferroelectric platforms requires on‐chip photodetection that combines wavelength selectivity, self‐powered operation, and material compatibility. We demonstrate a lithium niobate (LN) photodetector achieving these capabilities through synergistic integration of ferroelectric domain engineering and guided‐mode resonance (GMR) metasurfaces. Using focused ion beam milling on z ‐cut thin‐film LN, we create a continuous network of conductive domain walls (CDWs) at pillar‐trench interfaces while simultaneously defining a metasurface array that localizes the optical field at these same locations. This synergy enables efficient photocarrier collection directly within the conductive pathway. The device exhibits a resistivity reduction of up to 9 orders of magnitude compared to pristine LN and achieves self‐powered photodetection across the visible to near‐infrared spectrum (473–1900 nm). By tailoring the metasurface period, the response peak can be precisely tuned from 1550 to 637 nm, with responsivities reaching 0.11 A/W at zero bias and 31.8 A/W under 3 V bias. Using detectors resonantly tuned to distinct wavelengths, we demonstrate wavelength‐selective imaging with each detector responding exclusively to its target wavelength. The design leverages intrinsic ferroelectric properties, offering a material‐based pathway toward integrated photodetection in LN and other ferroelectric platforms.