| The unique bandgap structure of graphene makes it possible to generate photo-generated electron-hole pairs in a wide frequency range from ultraviolet to mid-infrared.The optical transition inside graphene can broaden the absorption range to far-infrared,even to terahertz Band.Excellent optical properties and conductivity make graphene has a broad application prospects in the photoelectric detection.The silicon-based detectors on the market have certian technical bottlenecks,like weak detection signal,a narrow range of detection(300-1100 nm),etc..So how to improve the performance of silicon based photodetector is an urgent problem to be solved.Chemical doping is one of the most popular doping methods to improve detector's performance,but it is unstable and may cause damage to graphene during the doping process.Due to the abundant storage and non-toxicity of silicon materials,nanoscale silicon-silicon quantum dots(Si-QDs)as another most important type of semiconductor,have gained more and more attention recently.The quantum confinement effect reveals that when the radius of silicon quantum dots is below the Bohr radius,it may have different electron band structures and luminescent properties from of the bulk silicon,which makes the silicon quantum dots become an extremely important fluorescent material.And the boron doping of silicon quantum dots has a strong absorption peak in infrared band.These characteristics make quantum dots has potential in photodetection applications.In this paper,the interaction between Si-QDs and graphene was studied by using two devices,to improve the performance of the photodetector.The main results are as follows:1.The working principle of Gr/Si Schottky junction photodetector is studied.The graphene/silicon forms a Schottky shallow junction at the contact interface.After the incident light is irradiated,the hole transfer to the graphene,andelectrons are collected by silicon,producing a photogenerated current.The relevant parameters of the Gr/Si Schottky junction are calculated by fitting the data with theoretical models.On the basis of this process,the performance of the Gr/Si detector is optimized by quantum dots,and the Si-QDs/Gr/Si photodetector with excellent device performance are fabricated.When the incident light wavelength is 405 nm and the power density is 0.1 mW/cm2,the photocurrent is 91 nA,and the responsivity is about 0.36 A/W.At the same time,we also tested the response time of the device and found that the time is less than 25 ns.2.On the basis of the Si-QDs/Gr/Si detector preparation process,we simplified the process flow,transferred the graphene to a silicon oxide substrate and patterned,then spin-coated quantum dots,to obtain boron-doped silicon-quantum-dots/graphene ultra-high gain and braodband photoconductive.Its working mechanism is:B-SiQDs n-type doped graphene when it was spin coated on graphene,and p-type doped under illumination,increased the light absorption of graphene,and improved the performance of the device.The response is about 109 A/W(incident wavelength is 532 rum,and power density is 0.2 g.W/cm2),and gain is as high as 1012.The response is also very high in the wavelength range 2.6-3.6 ?m,mainly due to the strong local plasmonic effect(LSPR)of B-SiQDs in mid infrared,which greatly broadens the detection range of the silicon-based photodetector and realizes the detection of silicon-based in the mid-infrared band. |
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