High-performance hot-electron sensing with planar Cu-ZnO junctions

Optical sensors quantitatively give the change of environment by interrogating spectral shift caused by the change in analyte refractive index. Herein, we present a design of hot-electron sensors to detect the change of analyte by direct readout without relying on the terminal optical equipment. The designed device consists of a one-dimensional TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> grating and an optically thick Cu layer separated by a ZnO film. Using suitable structural parameters, the designed device exhibits nearly perfect absorption at resonance wavelengths that can be tuned by grating periodicity. Detailed optical analysis demonstrated that the absorption efficiencies of the designed device are strongly related to grating filling factor. Electrical assessment indicates that the high responsivity is due to strong absorption in Cu and reduced Cu-ZnO barrier height (0.45 eV). Sensing performance in electrical sensitivity is up to 130.58 mA/W/RIU (RIU: refractive index unit). Moreover, the tunability of electrical sensing performance are emphasized by investigating the dependences of electrical sensitivity on the analyte refractive index and grating periodicity.