Studies On Surface Plasmon For Infrared Photodetection

The development of chemical preparation and micro-nano fabrication accelerates the study of plasmonics over the past decade. The wavelength of surface plasmon (SP) at the surface of metallic nanostructures was much shorter than that of the free light. So the electromagnetic fieds can be confined smaller than the free space wavelength, leading to near field enhancement at sub-wavelength dimension. Based on this, the plasmonics was important in applications at nanolithography, nanophotonics, biosensing, photodetection and so on. In the fields of photodetection, on the one hand, the metallic nanostructures can be used as antennas for traditional photodetector, on the other hand, the hot electrons generated from the SP resonance can be directly extracted for photodetection. But, the operating wavelength of SP resonance was usually in the visible region and can hardly be extended to infrared. Thus, it is a challenge to design plasmonic antennas and plasmonic hot electron photodetectors in the infrared region.In this thesis, we used the Finite Difference Time Domain (FDTD) and other numerical calculation methods to investigate and design split bull's eye (SBE) antennas that have much better performance than the traditional bull's eye (BE) antennas and Si-Au resonator based plasmonic hot electron schottky photodetectors with high responsivity at infrared. The main achievements in our work including:1. We systematically analyzed the enhancement mechanisms of the SBE antenna, which exhibits far greater transmission enhancement than the BE antenna. The improvement of the SBE antenna was substantially due to the transmission mode changing from evanescent to propagating, the induced Fabry-Perot resonances in the central slit and also the concentration capability of circular grooves. Moreover, we extended the operating wavelength of the SBE antenna to mid-infrared region, and the transmission enhancement of the SBE antenna can be enhanced by 6 orders than the BE antenna at the wavelength of 4 ?m.2. We proposed the dual split bull's eye (DSBE) antenna which has two crossed slits as central aperture, and the polarization dependence of the DSBE antenna can be tailored by adjusting the intersection angle of the slits. When the two slits are orthogonal to each other, the DSBE antenna was completely polarization independent. Furthermore, the transmission character of the DSBE antenna was similar as the SBE antenna, so its transmission enhancement was larger than the BE antenna in the infrared region. Thus, the new antenna structure can be used for the photodetection of unpolarized light or arbitrary polarized light in the infrared region.3. We established a complete numerical simulation method for plasmon-induced hot electron photodetectors including light absorbance, hot electron generation and hot electron collection. This simulation method can get more accurate responsivity of the photodetector, because it considered the specific distribution of the light absorption which was simulated by the FDTD.4. We designed a hot electron photodetector based on Au-Si resonator structure at the telecom wavelength (1550 ?m). The Au part of the photodetector can absorb 98% total incident light power. Furthermore, the responsivity of the photodetector is relatively high, because more of the hot electrons induced by the SP resonance can be transformed to photocurrent.