Modulation And Characterization Of Physical Properties Of Epitaxial Graphene On Silicon Carbide With Boron Ion Implantation

Graphene is a single atomic layered quasi-two-dimensional material with sp~2hybridization of covalent bonds between carbon atoms,its band structure shows a unique Dirac cone,whose upper and lower halves are symmetrically taken by the conduction band and valence band,respectively,and whose energy versus momentum exhibits a linear dispersion.Therefore,the perfect graphene has extremely high carrier mobility and excellent optical and electrical properties even at room temperature.However,as a zero band gap material,its application prospects are quite limited,such as in the fields of semiconductors and logic circuits.Fortunately,the state density of graphene near the Dirac point is limited.It’s conveniently to modulate its Fermi level by suitable methods,or realize the inversion of carrier type,and even open a band gap.All of these advantages provide the possibilities for the applications of graphene in electronic devices.Epitaxial growth of graphene on silicon carbide(Si C)is a preferred solution for the preparation of graphene-based devices.It can not only prepare large area of wafer sized high quality graphene and doesn’t need any further transfer processes for preparing graphene devices,but also the processing technology is compatible with modern semiconductor industry.However,epitaxial graphene on the(0001)oriented silicon carbide substrate is generally showing n-type conductive features due to the influence of the buffer layer.If the Fermi level of epitaxial graphene can achieve effective control by doping the beneath silicon carbide substrates,then it’s likely to epitaxial growth of p-type graphene on the(0001)oriented Si C substrates.In addition,applying some masking technologies as making a patterned doping of the Si C substrates may realize a periodic modulation in carrier types of epitaxial graphene(like in-situ epitaxial growth of graphene P-N junctions or other periodic structures),which will provide the possibilities of develop new devices with novel characteristics.In this work,patterned modulation of the carrier types of the epitaxial graphene on Si C was realized by adopting the method of ions(Boron(B)or Aluminum(Al))implantation combined with masking technology to dope the Si-face of 6H-Si CModulation and characterization of physical properties of epitaxial graphene on silicon carbide with Boron ion substrates.What’s more,we succeed in in-situ growth of graphene P-N junctions,which ultimately contribute to the successful preparation of a self-powered high-performance graphene ultraviolet detector.The main research results are as follows:1.After annealing the B ion implanted Si-face Si C substrate at a temperature about 1300℃-1400℃,we found that the lateral diffusion length of implanted B ions in the Si C substrate is larger than 2 microns,but smaller than 5 microns.However,the lateral diffusion effect of the implanted Al ions in the Si C substrate is not obvious.These results provide valuable parameters for designing the Si C-based MOSFET devices with minimum channel length by B ion implantation.2.We systematically studied the effects of B ion implant conditions on the transport characteristics of epitaxial graphene on Si C substrate,and obtained the optimal B ion implant condition for realization of the controllable epitaxial growth of p-type graphene on the Si-face of semi-insulation 6H-Si C(0001)substrate.In addition,we found that the reasons of obtaining p-type carriers in epitaxial graphene may be attributed to the synergy functions of the following two effects:(1)Substitution of B atoms in the graphene lattices;(2)The built-in electric field between the epitaxial graphene and p-type doped Si C substrates drives the electron carriers of graphene into the Si C substrate,so that the carrier type involved in the conduction of graphene are holes.Our experimental results show that this doping down-shifts the Fermi level of epitaxial graphene or even reverse its carrier type,regardless of the differences of Si C substrates polymorphous and orientations.What’s more,this method is also compatible with modern semiconductor processing technology,and provides a new way effectively and conveniently to fabricate of graphene P-N junction or other devices containing periodical p-type or n-type structures.3.Based on the P-N junction in the graphene layer,a self-powered graphene UV-enhanced photodetector was demonstrated,by combining the excellent physical properties of epitaxial graphene,silicon carbide and P-N junction in the same device.Because graphene and Si C substrate have different band-edge configurations in the surface layer of the ion implanted area and the non-implanted area,the largest surface potential difference of 210 m V was achieved on the graphene P-N junction.When an ultraviolet laser is locally irradiated on the P-end of a photodetector on the graphene P-N junction,the photoresponse to ultraviolet laser is 6 times larger than that of irradiated on the N-end.It indicates that the epitaxial graphene grown on the Si C substrate with p-type conductivity is more suitable for the preparation of high performance self-powered graphene-based ultraviolet detectors.Here the Si C substrate only acts as a gain medium.It’s further suggested that controllable in-situ growth of graphene lateral P-N junctions on periodic ion-implanted Si C substrate is a simple,effective and convenient method.More importantly,the preparation scheme proposed in this thesis can be fully compatible with the preparation processes of the modern semiconductor industry.At the same time,it provides the possibilities and significant reference for preparing devices of graphene P-N junction or other two-dimensional materials with novel physical characteristics.