ITO metasurface assisted quasi near-field focusing for enhanced photoresponse in ZnO photodetectors

Metasurfaces enable engineering of amplitude, phase, and polarization of incident electromagnetic waves, thereby providing robust control over their intrinsic properties. This has resulted in development of ultra-compact optical devices. Indium tin oxide (ITO) is used as an electrode in various optoelectronic devices. Integration of ITO metasurfaces with optoelectronic devices can eliminate the need for additional layers, as they can simultaneously serve as transparent electrode along with light-trapping element. Here, we report design and fabrication of ITO metasurface to concentrate UV– visible light (∼350 nm to 550 nm) in the quasi near field. ITO metasurfaces in form of square patches measuring 1.3 µm on each side, with thickness of 120 nm, and a periodicity of 2 µm were fabricated using femtosecond laser-based direct writing. The periodic arrangement of ITO patches facilitate the formation of electric field hotspots in the quasi near field due to the constructive interference of the diffracted light and guided mode resonance. We incorporated these metasurfaces onto ZnO quantum dots-based UV photodetectors, which exhibited about 183 % enhancement in the photoresponsivity due to the enhanced light-matter interactions. The proposed work highlights the potential of ITO metasurfaces as a promising technology in the development of high-performance, ultrasensitive photodevices.