Polarization-sensitive UV detector based on a double-layer subwavelength grating of Al and ZnO

Abstract

Polarization-sensitive detectors are of great importance in the fields of remote sensing and imaging, environmental monitoring, and medical diagnosis. The surface plasmon effect can the enable polarization sensitivity of photodetectors through metallic gratings. However, limited by the precision of the nano-fabrication process, it is difficult to fabricate an ultraviolet (UV) polarization-sensitive detector integrated with sub-wavelength metal gratings and the polarization extinction ratio is relatively low. In this paper, an Al–ZnO composite double-layer grating structure was designed. The ZnO active layer and the Al layer were both fabricated into same-sized grating structures. Through this design, the slit width could be enlarged to some degree, while the response to 90° polarized light remained low. It is beneficial to realize a high polarization ratio and to spare the need for rigid fabrication accuracy. In addition, the influence of the structural parameters of the grating on the performance of the detector was studied by simulation. It was found that the resonance wavelength can be adjusted by changing the slit width and grating height, respectively. This provides a useful means for polarization-sensitive detection in different wavelength ranges. The polarization extinction ratio of the detector with a double-layer composite grating can reach 52 in the UV band (365 nm). This provides a good alternative to replace the traditional framework relying on the combination of polarizers and detectors. Moreover, it is a promising structure for high-density integrated photodetectors and imaging chips in the future.