Structure Control And Performance Of Graphene/SiC Thin Films By Laser CVD

As a third-generation semiconductor,SiC has the advantages of wide bandgap,high saturated electron drift rate,high thermal conductivity,and good physical and chemical stability.It has huge application potential in high temperature,high frequency,high power and other semiconductor devices.However,the high cost of preparing SiC in a large area at present greatly limits the wide application of SiC.The preparation of 3C-SiC thin films by heteroepitaxial growth on Si is an effective way to realize large-area,low-cost preparation of SiC.Improving the crystalline quality of SiC epitaxial films and reducing the defect content of the films are very important for the subsequent preparation of high-performance SiC devices.Growing epitaxial graphene on SiC can take advantage of graphene’s high carrier mobility and high conductivity.It is also compatible with SiC semiconductor technology and can be used to prepare field effect transistors,photodetectors,etc.However,the crystal quality and growth area of epitaxial graphene grown on SiC need to be further improved,and the relationship between material structure and electrical properties needs to be further analyzed.Graphene/SiC composites can also be used as electrode materials in extreme environments due to their excellent physical and chemical stability,such as in the field of electric double layer energy storage.However,for existing Si-based electric double layer capacitors for energy storage,the capacitance and cycle stability of the electrodes still need to be further improved.The main research contents and results of this paper are:Epitaxial 3C-SiC films have been fabricated on Si（001）by laser chemical vapor deposition using hexamethyldisilane as source precursor and H₂as a dilution gas.In order to reduce the defects in the epitaxial film,the effects of H₂flow rate,off-angle substrate and inverted pyramid substrate on the twin density and reverse domain grain boundaries in 3C-SiC films were studied.Crystallographic defects,mainly composed of{111}twins that titled 15.8°to the surface of the substrate which referred to the multiple twins mirrored by the first order twins,were characterized by pole figure.With the flow rate of H₂increased from 1.0 to 3.0 slm,the relative twin density was decreased from 24.0 to 1.2 firstly and then increased to 16.0.As the off-axis angle of the Si（001）substrate increases from 0°to 4°and 8°,the g value（anti phase boundaries）of the electron cyclotron resonance of the SiC thin film first decreases from 2.00439 to 2.00434,and then increases to 2.00441.After growing an approximately 1μm SiC thin film on an inverted pyramid-shaped Si substrate with a side length of 18μm,the defects in the thin film began to decrease.The NCs were in situ grown on SiC films subsequent to the growth of SiC films by laser chemical vapor deposition.The results show that under the irradiation of a600 nm xenon lamp,the photocurrent response is proportional to the oxygen adsorption sites,and the oxygen adsorption sites are closely related to the sheet resistance of the sample,which can be adjusted by varying the reaction duration.The photocurrent of NCs grown on 3C-SiC was increased by 127%at a maximum sheet resistance of～26600Ω.We demonstrate the growth of large-area（～10×5 mm²）,high-quality（D/G area ratio:～0.03）epitaxial graphene on 4H-SiC（0001）using a high-power continuous laser with an extremely fast heating rate of 500°C/s.As the growth temperature rises from 1550°C to 1780°C,the number of graphene layers increases from three to more than ten.The obtained graphene/SiC samples are highly conductive,with a sheet resistance of as low as～0.43Ω/sq.The high power and fast heating rate of the laser contribute to the formation of large-area and low-sheet-resistance graphene.In this work,we rationally designed high-crystalline graphene/SiC（G/SiC）nano-matrix on the surface of planar Si and Si nanowires（Si NWs）array by laser chemical vapor deposition.The surface of Si NWs was fully covered with the G/SiC passivation layers,which composed of highly<001>-orientated 3C-SiC with graphene distributed in the films and the outermost layer.Compared to the Si NWs and planar G/SiC/Si structures,the G/SiC/Si NWs nano-matrix exhibited a low charge transfer resistance of 3.1Ω,and a high areal capacitance value of～3.2 m F/cm²achieved at a CV scan rate of 50 m V/s,nearly 10 times and 75 times higher than those of Si NWs and G/SiC/Si,respectively.The capacitance of the G/SiC/Si NWs nano-matrix was increased by 115%after 10000 cyclic voltammetry cycles at 100m V/s,showing excellent cyclic stability.