Fabrication Of Graphene Material And Application In Photodetector

As the theoretical and experimental studies on graphene become growingly thorough,its excellence in optoelectronic performance and stability at room temperature has emerged.Therefore,graphene has become one of the focuses of nanomaterial research in the past decade.The study of graphene materials and related fields is full of enthusiasm.Graphene nanowalls?GNWs?is three-dimensional materials formed by the vertical growth of graphene.Not only does it maintain the zero band-gap and layered structure of graphene,but it keeps the wide-band absorption characteristic ranging from visible light to terahertz as well.Moreover,the problem of weak absorption has been solved.The large-area and low-cost preparation of GNWs has been widely applied in uncooled,high-responsivity and broad-spectrum photodetectors.In this paper,a high-performance graphene nanowalls/silicon?GNWs/Si?heterojunction photodetector is prepared by in-situ growth of GNWs on silicon.Firstly,the photoelectric properties of GNWs and the photoresponse of GNWs/Si heterojunction in visible light were studied.Then the surface charge transfer doping technique was used to control the work function of GNWs to study the hot carrier emission mechanism and infrared photoelectric response characteristics of GNWs/Si heterojunction photodetectors.The main research contents and conclusions include:?1?GNWs film was prepared and characterized.GNWs films with different growth time were prepared by radio frequency plasma enhanced chemical vapor deposition?RF-PECVD?.The morphologies of GNWs films were observed by scanning electron microscopy?SEM?,Raman spectroscopy,transmission electron microscopy?TEM?and high-resolution transmission electron microscopy?HR-TEM?.The structure was characterized and analyzed briefly.The relation between the square resistance and transmittance of GNWs film and growth time was studied by four-probe method and UV-visible spectrophotometer,and further verified by Raman spectroscopy.?2?The photoelectronic properties of GNWs/Si heterojunction photodetectors were researched.A heterojunction photodetector with high-quality interface was prepared by in-situ growth of GNWs on silicon.The photoelectronic response in the optical band was tested.Responsivity of 0.52 A/W,on/off ratio of as high as 2×10⁷,time response of 40?s were obtained.The device also has a high linear dynamic range of 105 dB and a 3dB cut-off frequency of 8.5 KHz.Using the Fast Fourier Transform?FFT?system to test the device,the ultra-low noise current spectrum of 3.1fA Hz^-1/2 and the specific detectivity of 5.88×10¹³ cm Hz^1/2/W are realized,which is the maximum specific detectivity based on measured dark current noise so far.The ideal factor of 1.18 and the barrier height of 0.69 eV are obtained by the Schottky junction model fitting,which theoretically explains the reason for the low dark current.?3?The hot carrier emission mechanism and infrared photoelectric response characteristics of GNWs/Si Schottky junctions were investigated.The irregular gold?Au?nanoparticles were prepared by thermally annealing the Au film on the silicon.The surface charge transfer doping technique was used to adjust the work function of GNWs.By analyzing the optical response of GNW/Si photodetectors with different structures,different metal nanoparticles and different GNW growth times,we found that the 20 min GNW/2 nm Au/Si heterojunction photodetector has the highest responsivity at 1550 nm.The responsivity can reach 138 mA/W.Subsequently,the Au nanoparticles were modeled and analyzed.The resonance peak after annealing at 2 nm gold film appeared in the region around 1500 nm,which was consistent with the experimental results.The introduction of Au nanoparticles reduces the barrier height and enhances the emission efficiency of hot carriers.The device's detectivity is increased to 1.4×10¹⁰ cm Hz^1/2/W,the on/off ratio is up to 10⁴,and the time response is 370?s under the wavelength of 1550 nm.The responsivity of the device is 0.44?A/W at 0 V in the 3.5?m band.The study of GNWs hot carrier emission mechanism and the implementation of high-performance photodetector components provide a new idea for the development of infrared high-efficiency photoelectric conversion devices.