Design And Fabrication Of Three-dimensional Photodetector Based On Single Wall Carbon Nanotubes/Graphene Heterojunction

As an important means of photodetection,photodetectors play an important role in aerospace detection,military reconnaissance,national life,and other fields.Although traditional silicon-based photodetectors show the advantages of mature fabrication technology and low cost,the wide band gap（≈1.12 e V）of silicon materials limits their applications in the visible and near-infrared bands.In recent years,graphene-based photodetectors have attracted widespread attention due to their ultra-wide optical bandwidth and ultra-fast optical response speed.However,the low light absorption rate（～2.3%）of the single-layer graphene and the fast photo-generated carrier recombination rate make the photoresponsivity of graphene-based photodetectors extremely low（m A/W）,which greatly limits their applications.In this thesis,a single-walled carbon nanotubes（SWCNTs）/graphene heterojunction,integrated with a three-dimensional（3D）optical resonator microstructure was proposed.By using MEMS processing technology,a 3D optical resonant arrayed photodetector based on SWCNTs/graphene heterojunction was fabricated and demonstrated.The combination of heterojunction and 3D structures effectively improves the photoresponsivity of graphene-based photodetectors.The main research contents of this thesis are as follows:1.The realization of the mass and stable fabrication of 2D and 3D graphene/SWCNTs heterojunction photodetectors.By applying the self-folding technique,the SiN_x stress layer would drive the buried-gate planar（2D）SWCNTs/graphene heterojunction photodetector to form a 3D resonant microcavity photodetector,due to the stress difference generated after the sacrificial aluminum（Al）layer being etched away.It has been detected that the device area for the 3D structure is effectively reduced by more than about 80%compared with the 2D counterpart.464array units can be obtained on a silicon wafer with a size of 1.5 cm×1.5 cm,where each unit contains 5 FET devices.2.The exploration of the photoresponse for 2D graphene/SWCNTs heterojunction photodetectors within different wavelength bands.Within the ultraviolet band,the mechanism of the 2D device is mainly based on the O₂ adsorption and desorption effect,with a photoresponsivity of 204.5 A/W.Within the visible and near-infrared bands,it works based on the photogating effect with a photoresponsivity of 109 A/W.The photoresponsivity is expected to be further improved by shortening the conductive channel length.3.The investigation of the photoelectrical performance of the 3D graphene field effect transistor（GFET）photodetector.Under the irradiation of incident light with a wavelength of 514 nm,the photoresponsivity is increased by more than 1000 times compared with that of the 2D GFET.Moreover,under the influence of the 3D resonator,the 3D GFET exhibits polarization sensitive properties due to the 3D resonator structure,with a polarization ratio of 1.2.4.The exploration of the photoresponse for the 3D graphene/SWCNTs heterojunction photodetectors in different wavelength bands.Within the ultraviolet band,the photoresponsivity of the 3D device is 8.5 times higher than that of the 2D device.Furthermore,the photoresponsivity of the 3D device within the visible light band is as high as 4220 A/W,which is 10.4 times higher than that of the 2D device.Within the near-infrared band,the 3D photoresponsivity is 1336 A/W.The 3D optical resonant microcavity would not only enhance the internal optical field,but also increase the light absorption of heterojunction film,due to the incident light reflected back and forth in the microcavity.Hence,the photoresponsivity is significantly improved.In summary,the method of constructing graphene/SWCNTs heterojunction and integrated with 3D optical resonant microcavity effectively improves the photoresponse of graphene-based photodetectors.Meanwhile,the device area has been reduced.This approach provides new research ideas to achieve miniaturized,integrated and high-photoresponse photodetector with high-performance.