Epitaxial Growth And Structure Characterization Of SiC Film And Fabrication Of Graphene

As a wide-band gap semiconductor material with excellent properties,SiC has many applications in the field of the semiconductor devices.Graphene,comprising of monolayer of carbon atoms packed into a two-dimensional honeycomb lattice,has a series of peculiar properties such as the anomalously quantized Hall effects,the large charge carrier mobility and so on.These peculiar properties have been promoted people to be interested in the graphene research.In this thesis,we report that the SiC films grown on different substrates of Si,SiC and Al₂O₃ and the quantum wells structure based on SiC polytype grown on 6H-SiC single crystal substrates have been produced with the method of solid source molecular beam epitaxy(SSMBE).Besides, the graphene films have also been grown on SiC surface by using the method of thermal annealing at high temperature and assisting with Si flux in the MBE chamber. Synchrotron radiation(SR) experimental technics and some normal analysis methods have been employed to investigate the grown SiC and Graphene films.The main results are listed as following.1:The epitaxial growth of 3C-SiC films on Si substrateThe 3C-SiC films with high quality have been hetero epitaxially grown on Si substrate by the method of SSMBE.The effects of the growth factors,such as carbonization,growth temperature,Si/C flux ratio,and Ge predeposition,on the quality of SiC film have been investigated systematically and the optimized parameters have been obtained.1) The carbonization of Si surface can accommodate the lattice mismatch,reduce the stress and improve the quality of the films.The optimized carbonized temperature is obtained on the basis of the studies above.2) The quality of the film grown at the substrate temperature of 1000℃is the best. With higher substrate temperature,the misfit of thermal expand coefficient between SiC film and Si substrate can cause the dislocations at the interface, which affects the quality of the film.However,with lower substrate temperature, the activity of atoms is lower,thus the atoms have not enough energy to move and can not arrive the favorite positions for the growth of films,which causes the quality of the film worse.3) The quality of the sample with the optimized Si/C flux ratio(1.5:1) is the best and the qualities of the samples with higher Si/C flux ratio(2.3:1) or lower Si/C flux ratio(1.1:1) are worse.Controlling the Si/C flux ratio can suppress the voids and improve the quality of the SiC film.4) Ge predeposition can improve the quality of SiC film grown on Si substrate.We have optimized parameters of the amount and the temperature of Ge predeposition. The Ge predeposition induces the formation of the Si_1-x-yGe_xC_y solid solution at the interface,which acts as the intermediate buffer layer to accommodate the lattice mismatch,reduce the accumulated strain of the interface and improve the quality of the SiC film.2:The growth of 6H-SiC films on Al₂O₃ substrate1) The 6H-SiC films have been hetero epitaxially grown on Al₂O₃(0001) substrate by the method of SSMBE.X-rayΦscan shows the six-fold symmetry of SiC(100) planes,which indicates that the grown SiC thin film is almost the single crystal film.2) The quality of the film grown at substrate temperature of 1100℃is the best and that of the films grown at substrate temperature of 1000℃and 1200℃are worse.3) The results of GID show that the films are under compressive stress caused by the misfit of the thermal expand coefficient between SiC film and Al₂O₃ substrate. When the internal part of the film is further away from the interface of SiC film and Al₂O₃ substrate,the strain of the SiC film decreases and the crystalline quality of the SiC film becomes better.The results of XRD and GID show that the film has different tilt mosaic and twist mosaic and the angle distribution of former is smaller than that of the latter.3:Homoepitaxy growth of SiC film and the fabrication of SiC polytype quantum wells on 6H-SiC(0001) substrate1) After Si predeposition,the surface structure of 6H-SiC(0001) changes with the variation of substrate temperature.When the temperature increases,the evaporation of Si atom from the surface causes the Si atoms on the surface gradually decreases.Thus 3×3 and 3^1/2×3^1/2 reconstruction can be obtained.(2) Due to the difference of diffusion coefficient of Si atoms on the different reconstruction surfaces,the 3C-SiC and 6H-SiC films have been successfully grown on 3×3 and 3^1/2×3^1/2 reconstruction surfaces of 6H-SiC(0001) substrate respectively by controlling the Si flux at substrate temperature of 1080℃.(3) The 6H-SiC/3C-SiC/6H-SiC film with quantum wells structure has been fabricated on the 6H-SiC substrate by controlling the flux at the substrate temperature of 1080℃.The intense emissions are found in a wide range of spectrum,which is attributed to the luminescence of the 6H-SiC/3C-SiC/6H-SiC quantum wells.The calculated results show that the wide range of luminescence is probably caused by the quantum wells with different width.4:The growth of graphene on SiC surface1) The epitaxial graphene(EG) layer has been successfully grown on Si-terminated 6H-SiC(0001) substrate by the method of thermal annealing at high temperature and assisting with Si flux in ultrahigh vacuum(UHV) molecular beam epitaxy(MBE) chamber.2) The effect of annealing time on the growth of graphene on 6H-SiC(0001) surface is investigated.With the increase of annealing time,the thickness of graphene layer increases and the voids on the grown graphene surface decreases.There is compressive strain in the film,which is induced by the large difference between the coefficients of thermal expansion of graphene and SiC.The strain of the film becomes smaller with the increase of the layer thickness.