| The absorption spectra of plasmonic structures are tunable by changing characteristic parameters.The excited plasmons can transfer photon energy into electrons in metal through nonradiatively decaying and generate‘hot’ carriers.Those hot carriers have enough kinetic energy to overcome Schottky barriers and can be injected into the semiconductor channel,which makes sub-bandgap photodetection possible regardless of the forbidden gap.Hence,the hot-carrier photodetectors based on plasmon resonances are competitive in infrared photodetection.On the other hand,when plasmon-induced hot carriers are used as injected excess carriers for photodetection,the polarization selectivity of plasmonic structures will be introduced to the photodetectors,making it feasible to realize polarization photodetection.Although hot-carrier infrared photodetector based on plasmonic effect exhibits many advantages,the responsivity is still much lower than conventional photodetectors because of the very low injection efficiency.In this thesis,the infrared photodetections based on 2D WSe2 and hot carrier effect of plasmonic resonance is studied,and the corresponding fabrication and testing of the devices are carried out,in order to achieve the high responsivity and high polarization sensitivity.The research contents are as follows:1)From the fabrication point of view,to overcome the difficulties of electron beam lithography on insulating substrates(such as quartz)or 2D materials(such as WSe2),a transfer technology is proposed,which can be adapted to transfer nanostructures prepared on SiO2/Si onto any substrates without damages.This process lays a foundation for the preparation of nanostructures/2D material hybrid structure.2)The photoresponsivity of hot-carrier photodetector is limited by the low injection efficiency of hot carriers and the lack of gain.To solve this problem,we propose an infrared hot-carrier photodetector with high gain by stacking 2D plasmonic gold nanodisk arrays on multilayer WSe2 transistor.The surface plasmon resonance is excited to enhance the absorption of infrared light,resulting in an absorption higher than 90%in the band of 1100～1600 nm.The hot carriers generated by gold nanodisks are injected as excess carriers into multilayer WSe2,drifting in the lateral external electric field and forming a photocurrent.As a result,the responsivity is as high as 4 A/W,accompanied by a high gain up to 1.25x 104.The performance of this device breaks the limit of low injection efficiency.3)Finally,an advanced study on polarization photodetection is performed.In regard to the detection of circular polarized light,a plasmonic chiral metal/insulation/metal structure is demonstrated via numerical calculation and optical simulation.Unlike the gold nanodisk array as mentioned above,the chiral structure is sensitive to circular polarized light.By hot carrier injection,the detection of circular polarized light is elementarily realized at this stage.For linearly polarized light,a quasi-BIC metal structure is designed in this paper,which is sensitive to linearly polarized light and shows a narrowband absorption.The fundamental mechanisms are further analyzed,and this quasi-BIC metal structure shows great promise for linearly polarization photodetectors. |
