The Defects Recovery And Raman Spectroscopy Study Of Neutron Irradiated6H-SiC

Raman spectroscopy is an effective and nondestructive detection method foranalysis of materials and material defects. In this paper, we firstly calculatedtheoretically the vibration modes of6H-SiC by using the space group theory and theanalysis of large-zone and zone folding model. Based on the above theorical results,Raman spectroscopy of neutron-irradiated and post-annealed6H-SiC crystal aredetected and analyzed. We also studied the damage and annealing recovery ofirradiated6H-SiC with different doses using UV-Visible spectroscopy and X-raydiffraction for identifying the irradiation damage level and recrystallinity with theannealing temperature. The main studies and contributions of this paper are asfollows:1. The damage and annealing recovery of neutron irradiated6H-SiC with fluenceof1.67×1019n/cm~2and1.72×1020n/cm~2were investigated by Raman technique. Thedamage level increased with increasing fluence in irradiated6H-SiC which probablycontained localized amorphous domains. Graphite clusters can be observed in higherfluence irradiated6H-SiC with1.72×1020n/cm~2. The different frequency downshifttogether with the change of line shape of LO and TO band due to irradiation is mainlyattributed to the phonon confinement effect. The slight reduction of LO-TO frequencysplitting caused by irradiation could originate mainly from the isolated vacancies andinterstitials indicated from the evolution of LO and TO band with the annealingrecovery.2. The effects of irradiation and annealing treatment of sample are analysised byabsorption UV-Visible light. The red shift of absorption edge and the increase ofabsorption coefficient after irradiation are related to the formation of localized levelsnear the gap edges induced by the accumulation of radiation defects. The annealingbehaviour of absorption spectrum indicates the strong absorption fluctuation of bandedge are related to the light scattering induced by various types of complicated defectsclusters in irradiated crystals. Moreover, the absorption remains unchanged until800℃andbegins to decrease after800℃with increasing annealing temperature,which are concerned with the recovery of different types of defects.3. The change of the degree of lattice ordering caused by irradiation andpost-annealing is studied by X-ray diffraction (XRD) technique. We found that neutron irradiation leads to the decrease of the degree of lattice ordering and theincrease of full wide at half maximum (FWHM) of X-ray diffraction peak. However,the restarted increase of lattice ordered degree and FWHM shows the regular recoverywith increasing annealing temperature. Based on this law, a novel temperaturemeasurement technique can be developed for the determination of complicatedtemperature field.The annealing behaviour of neutron irradiated6H-SiC investigated using abovethree kinds of techniques reveals that approximately800℃isan importanttemperature point which according to the recovery and transform of irradiated defects.The recovery process observed in SiC may be associated with the recombination ofclose Frankel pairs and migration of interstitials before800℃annealing treatment.The recovery of crystallinity depends strongly on recrystallization of amorphousdomains and the recombination and annihilation of defects through the migrations ofvacancy and the dissociation decomposition of complicated defects clusters afterannealing at800℃. The irradiated defects almost recovered at annealing1600℃.