Design of a Surface Plasmon Resonance-Enhanced ZnO Ultraviolet Photodetector Based on a Sub-wavelength Metal Grating Covered with a High-Refractive-Index Medium

To realize a surface plasmon resonance-enhanced zinc oxide (ZnO) ultraviolet photodetector based on a sub-wavelength metal grating, we take advantage of the sensitivity of the resonance condition of a sub-wavelength metal grating to the refractive index of the surrounding medium. We theoretically design a sub-wavelength Ag grating covered with a high-refractive-index medium layer and apply it to a ZnO ultraviolet photodetector. By optimizing the parameters (angle of incidence, grating period, grating spacing, grating thickness, high-refractive-index medium layer thickness, refractive index of the covering), the optical field is localized at the interface of the sub-wavelength Ag grating and the ZnO thin film; that is, surface plasmon resonance is realized within the device. Compared with the device without a high-refractive-index medium layer, the maximum absorption enhancement factor of the designed device can reach up to 108. This work will provide theoretical guidance to realize a surface plasmon resonance-enhanced ZnO ultraviolet photodetector with a sub-wavelength metal grating.