Study On Growth And Contact Characteristic Of Large Domain Graphene

Graphene,due to its unique two-dimensional structure,has excellent electrical conductivity,high transmission,high mechanical strength and flexibility.It is a promising material and is widely used in many fields.At present,the growth of large crystal domain graphene is still a research hotspot,and oxygen plays an important role in the growth of large crystalline graphene.In the process of PMMA transfer graphene,there are a large number of residual particles on graphene surface,and graphene devices are susceptible to many contact factors.Based on the above background,graphene was prepared on copper film by CVD method,and the effect of oxygen treatment on the growth of graphene was studied.On the basis of oxygen treatment,some CVD growth parameters on graphene growth were studied.Then,the transfer method of graphene was optimized by using small molecu le MMA.Finally,the contact characteristics of graphene under various conditions were studied based on TLM model device.The research and results achieved are as follows:1.The three ways to participate in the growth of graphene were studied,namely,the heating oxidation of external CVD chamber,the oxidation before annealing and the oxidation before annealing in the CVD chamber.The experimental results show that the nucleation density of graphene in the copper foil reachs the smallest value of 0.1327 m m-2 when oxidation is introduced into CVD chamber before annealing,and the maximum speed is up to 47 μm.min-1 in the average diameter of the corresponding graphene domain.2.The effects of main growth factors on the nucleation density of graphene,such as growth temperature and hydrogen methane flow rate,were studied under the participation of oxygen.The growth of graphene by temperature showed that the nucleation density of graphene first increased and then decreased with the temperature increasing.At 1050 oC,the nucleation density of graphene was the lowest,and the growth rate of graphene increased CVD.The growth activation energy of graphene is 2.24 e V.The experiment of hydrogen methane flow shows that under the small flow rate of methane,the do main average diameter of graphene decreases with the hydrogen flow increasing.The size of single domain graphene increases with the increase of methane flow rate,and the ratio of methane to hydrogen gas for fast and large crystal graphene growth is 1:500 approximately.The growth rate of graphene nanocrystal domain shows that the domain of graphene grows at a constant rate,and the growth rate is 35.36 μm.min-1,and the nucleation time of graphene is 5.38 min.3.Transferring graphene with MMA indicates that MMA can transfer intact graphene as an auxiliary layer.Compared with PMMA assisted transfer graphene,MMA has less adsorption energy than graphene,and the unintentionally doped graphene has small concentration and small particle size,and has good surface flatness.Transmission studies of transferred layer-stacked graphene show that the transmittance of monolayer graphene is 97.01%,and the monolayer absorptivity of graphene is 2.44%.4.The factors affecting the contact characteristics of graphene,such as annealing conditions,selection of metal electrode materials,selection of insulating substrates and surface passivation of graphene,are studied.The annealing temperature range is 300 oC ~500 oC,and the contact resistance of graphene electrode decreases first and then increases with the increase of temperature.When the annealing temperature is 400 oC,the contact resistance of the electrode reaches the minimum,553.95 Ω.μm.Compared with that without annealing treatment,the contact resistance decreases 2.5 times.When the annealing time is in the range of 2~15min,the contact resistance of the electrode decreases first and then increases.When the annealing time is 9min,the contact resistance of the electrode is 787.55Ω.μm,and the minimum value is obtained.The optimized annealing condition is 400 oC and 10 min.The experiment of gold electrode and aluminum electrode shows that the contact resistance of aluminum electrode is 24 times larger than that of the gold electrode;the research on the contact characteristics of graphene with different insulating substrates shows that the contact characteristic of the graphene device with Si O2 and Al2O3 insulating substrate is better than Hf O2 and Zr O2 as insulating substrate.Surface passivation study of graphene device shows that PMMA can be used as passivation layer of graphene,thereby effectively enhancing the gate control characteristics of GFET devices.