Studies Of Ion-Irradiation Induced Damage In Single Crystal 4H-SiC

Due to the high melting point,high corrosion resistance,high heat conductivity and low neutron reaction cross section,etc,Si C materials are well suitable for advanced nuclear power plant with high temperature and high flux neutron irradiation environments.Displacement damage caused by neutron irradiation and helium and hydrogen atoms that are produced by neutron transmutation reaction,results in swelling and material embrittlement,which seriously affect the service life of the material.Therefore,futher study of He and H mutual effect mechanism is great important for Si C materials applied in future advanced nuclear energy system.The <0001>-oriented 4H-Si C single-crystal wafers were obtain from MTI compay.He,Si and H ion implantation/ irradiation experiments at room temperature were performed at 320 k V High-voltage Platform in Institute of Modern Physics,Chinese Academy of Sciences.The energies of He,Si and H ions are 230 ke V,880 ke V and 260 ke V,respetively.The fluences of He ions and Si ions are in the range of 1.0×1015 ~ 2.0×1016 cm-2(0.04-0.8 dpa,dpa: displacements per atom)and 8.13×1013 ~ 1.63×1015 cm-2(0.04-0.8 dpa),respectively.The fluence of H ions is 5.0×1015 cm-2.According to SRIM-2008 simulation,the projected range of He ions is the same as Si ions.The projected range of H ions is larger than that of He ions.The irradiation damage has been investigated by a combination of Raman spectroscopy,high resolution X-ray diffraction,and nano-indentation.The main research results are shown as follows:1.The intensities of Raman peaks decreased with increasing He fluences.The decrease of Raman peaks is related to the He irradiation-induced damage.The change of Raman peak intensities was simualted by DI/DS(direct impact/ defect simulated)model and MSDA(multistage damage accumulation)model.For He ion irradiation into 4H-Si C at room temperature,MSDA can fit very well the relationship of 4H-Si C damage accumulation and fluence change.At the stage of 0-0.04 dpa,the majority of damage were point defects.At the stage of 0.04-0.28 dpa,the damage process is the coalescence of point defects into dislcoation loops.At the stage of 0.28-0.32 dpa the damage process is that the numerous dislocation loops stimuated the formation of amorphization.At above 0.32 dpa,the damage process is the growth of amorphization.For high temperature He irradiation into 6H-Si C,DI/DS model results show that damage accumulation could be divided into two stages.Below 1 dpa,irradiation damage was mainly caused by extended defects.Above 3 dpa,irradiation damage was mainly caused by ion irradiation-induced amorphization.DI/DS model is good for high temperature damage accumulation process,while the MSDA model is good for room temperature damage accumulation process.2.The irradiation hardening is slight as the He fluences are 1.0×1015~ 6.0×1016 cm-2(0.04-0.24 dpa).Above 6.0 × 1016 cm-2,the irradiation hardening increased significantly,and the value of hardness was maximum at 1.0×1016 cm-2.Above 1.0×1016 cm-2,the value of hardness decreased.H ion irradiated the pre-He irradiated 4HSi C,the increase of Raman peaks and the decrease of hardness compared to those of He-implanted 4H-Si C.The results demonstrate that partial He irradiation-induced defects were annealed out during H irradiation.In addition,a new phase was formed after H ion irradiation.The result of HRXRD shows that the lattice strain near the sample surface decreased slightly after H irradiation.3.For the same dpa,the intensities of Raman peaks were weaker in the Si-irradiated 4H-Si C than that of He-irradiated 4H-Si C.At 8.13×1013 cm-2(0.04dpa),the irradiation hardening is significant.Above 2.44 × 1014 cm-2(1.2 dpa),the value of hardness decreased significantly.The intensities of Raman peaks did not change in the Siirradiated 4H-Si C followed by H irradiation,while the results of HRXRD show that the strain of the damaged layer increased slightly after H irradiation.