Preparation And Properties Of Photodetectors Based Graphene

Graphene based photodetectors have always been a research hotspot,especially graphene was combined with other materials to make different structures,showed excellent photoelectric characteristics;but graphene only acts as an electron collector in the device in most cases.In this paper,by designing MIS graphene photodetector and adjusting the structure of the device,we confirmed that graphene can regulate the photoelectric response,revealed the mechanism of photoelectric response,and improved the photoelectric characteristics of graphene photodetector.Graphene were prepared by chemical vapor deposition(CVD).Monolayer graphene were obtained by changing a series of parameters about process such as methane/hydrogen flow rate,annealing time and reaction temperature.The surface morphology,transmittance and composition hybrid mode of graphene were measured by ultraviolet visible spectrophotometer,optical microscopy and Raman spectroscopy;The film was transferred to SiO2/Si substrate by wet transfer method,and the photoelectric detection devices of MIS and MS junction were fabricated.The responsivity and switching ratio of the devices were tested.By comparing the characteristics of p-type and n-type devices and the influence of annealing on the photoelectric characteristics of the devices,the physical model of photoelectric response was established,and the physical mechanism of photoelectric response was studied.The results are as follows:(1)Under the conditions of methane flow rate of 30 sccm,hydrogen flow rate of 8 sccm,annealing temperature of 20 minutes and reaction temperature of 1030?,the single and high quilty graphene with few defects were obtained.The surface morphology of the graphene is complete,and the transmittance is 96.1%.There is no D peak in Raman spectrum,which proves that the defects are less in the graphene.The 2D peak at 2669.9 cm^-1 is high,and the line shape of composite Lorentz curve;the half peak width of G peak at 1577.3 cm^-1 is small,and I2D/IG ratio is 2.12,which is larger than the standard ratio of 2.(2)The results show that the dark current of MS junction device is obvious,reaching the mA level,and the switch ratio is very low,it is only 50.78 under zero bias voltage,while the switch ratio of MIS device can reach 10179.87 under zero bias voltage.The interface capacitance coupling effect controlled by the dielectric thickness and the graphene Fermi level lead to high responsivity and switching ratio.Finally,a graphene photodetector with a responsivity of 2.07 A/W and a switching ratio of 10179.87 is obtained.(3)The maximum photoelectric responsivity of MIS junction device can reach 2.07 A/W,and it can work stably in the range of 0.05 V to 5 V bias voltage.The photocurrent increases by 52.56%when the thickness of graphene increases from 1 layer to 10 layers;and the dielectric thickness decreases from 100 nm to 10 nm,with the highest responsivity of 0.38 A/W under the condition of monolayer graphene.(4)The increase of the silica thickness leads to the decrease of the parasitic capacitance and the corresponding carrier concentration,which leads to the decrease of the Fermi level deviation of graphene and the decrease of the built-in electric field,the responsivity decreases from 0.38 A/W to 0.13 A/W;the increase of graphene layers leads to the increase of carrier concentration,and the increase of tunneling probability by the enhancement of built-in electric field between graphene and silicon,the grating effect is formed to improve the responsivity through the coupling of external circuit;the doping type of the substrate and annealing change the built-in electric field and affect the response of the device.The work of this paper analyzes the photoelectron response mechanism of MIS junction graphene detector,which provides a basis for the wide application of graphene photoelectric devices in the future.