| In recent years,as one of the thinnest materials with the biggest mechanical strength that we have known,by the ultra-high electron mobility,good thermal conductivity,high transmittance and other characteristics,graphene has been paid great attention by researchers in various fields.Among the methods of producing graphene,using chemical vapor deposition(CVD)to prepare graphene is simple,the obtained graphene is of high quality and large area,so it has become the main method of preparing high quality graphene.However,due to the low melting point of the substrate material and the limitation of growth equipment,the growth temperature of graphene is only ~1000℃ in the conventional CVD method,and there are few reports on the growth of CVD graphene under ultra-high temperature conditions,which hinders A further understanding of the growth mechanism of graphene CVD is not conducive to the future research and application of graphene.In addition,CVD graphene as a transparent conductive layer(TCL)is one of the important fields of large-scale application of graphene in the industrial production of GaN-based LEDs.This is because CVD graphene can overcome the traditional ITO while maintaining the performance of TCL.A large number of defects caused by materials,however,the industrial application of CVD graphene still faces many problems.First,in order to avoid the non-ideal factors brought about by the transfer of metal substrates,graphite can only be grown on the surface of GaN epitaxial wafers by direct growth.Alkenes,while direct growth requires lowering the growth temperature to protect the GaN epitaxial wafer from damage,while the low catalytic properties of the GaN epitaxial wafer surface make graphene growth more difficult;secondly,in order to reduce the production cost,the growth time must be short enough,and the conventional CVD method requires at least several hours to complete the growth,which cannot be achieved.Based on this,it is necessary to study the CVD growth technology of graphene under special conditions for its early application in the industrial production of LED.In summary,the study of chemical vapor deposition of graphene under special conditions not only contributes to the development and improvement of the theoretical system of CVD graphene growth mechanism,but also has important practical application value.This paper mainly studies the chemical vapor deposition and transfer technology of graphene under special conditions.Firstly,the growth mechanism and transfer process of graphene under ultra-high temperature conditions were explored,and the semi-quantitative electrical model of graphene transfer graphene was established.The surface of graphene on p-GaN and Cu/p-GaN substrates was studied.The low temperature rapid growth process,LED devices were fabricated on two substrates after graphene growth,and the photoelectric properties of LED devices were tested and compared.Finally,the direct rapid growth of graphene on ITO surface under low temperature conditions was studied.This paper was supported by the Major National Science and Technology projects(No: 2017YFB0403100,2017YFB0403102)and Beijing Natural Science Foundation.The main research work and achievements are as follows:1.The growth mechanism of CVD graphene on the surface of refractory metal ruthenium(Re)and tantalum(Ta)under ultra-high temperature conditions(1200 °C-3000 °C)was clarified.Through the characterization and analysis of graphene,it is found that the growth mechanism of graphene on the surface of the crucible is similar to the mechanism of carbonization and carbonization of nickel.With the increase of growth temperature,the quality of graphene rises first and then decreases.However,"Ta-C compounds" are easily formed between the surface of tantalum and carbon,which has an important influence on the growth mechanism of graphene.The quality of graphene generally increases with the increase of growth temperature.In addition,graphene on the surface of ruthenium and tantalum is studied.Different methods of transfer have proposed a technical scheme for efficient transfer of graphene.2.The electrical model of graphene bubbling transfer method was established.the structure of metal/PMMA/electrolyte was simulated by capacitance element and the basic circuit of bubble transfer process was constructed.According to the circuit,a method of greatly reducing the transfer time of graphene is proposed,which can reduce the transfer time of graphene by more than 60%,then the Anodic electrolysis method was used to transfer the graphene successfully,which explained the reason that the cathode transfer was better than anode transfer.Finally,the effect of different electrolytes on the transfer process of graphene was discussed.The transfer mechanism of graphene could be explained semi-quantitatively by the electrical model of bubbling transfer method,which had positive significance for the development of transfer technology by bubbling method.3.The low temperature rapid growth of the graphene film on the surface of the GaN epitaxial wafer is realized.With the aid of plasma,low temperature rapid growth of graphene was performed on the surface of bare p-GaN and Cu(10 nm)/p-GaN substrates by cold-wall CVD,and it was found that the bare p-GaN surface only showed a diameter of ~20 nm.The carbon particles of nm and the macroscopic continuous graphene film on the surface of Cu(10 nm)/p-GaN have a grain size of ~160 nm.LED devices were fabricated on the above two substrates,and the latter was found to be obvious.With better optoelectronic performance,the operating voltage at 20 mA is reduced by approximately 16% even with LEDs using high quality transfer graphene for TCL.4.The rapid growth of graphene on the surface of ITO was studied for the first time.A thin layer of ITO(50 nm)was deposited on the surface of p-GaN to replace the traditional thick layer of ITO(240 nm)to achieve the purpose of reducing the amount of ITO.The surface of ITO(50 nm)/p-GaN was successfully grown continuously.The graphene film has a film thickness of ~6 nm and a nanocrystalline graphene size of 40-80 nm.To reduce the influence of the substrate,the application range of the technology is further expanded,and the graphene is on the ITO(200 nm)/p-GaN surface.The growth process was carried out.The results show that the surface of the above substrate grows carbon nanoparticle cluster structure under low temperature conditions.The average diameter of carbon nanoparticles is ~20 nm.A large number of cluster structures form a continuous carbon film on the ITO surface.The growth rate of the carbon film is positively correlated with the plasma power. |
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