Optical Properties And Defect Analysis Of6H-SiC Crystals Irradiated By Heavy Neutron

SiC, an important wide band-gap semiconductor, has attracted much attentionowing to its wide applications. SiC has strong irradiation resistance ability which playan important role in aerospace, nuclear power development etc. However under thecondition of irradiation, large number of defects were induced and its crystal structure,mechanical properties, electrical properties, optical properties, thermal properties willchange and have bad effect on the application. Therefore, It is very necessary to makefully understanding of the properties change of irradiated SiC. Defect can be removedand properties of crystal replied during the annealing process. So we used irradiationand annealing to study the properties change of SiC crystal. The TEM, UV-VIS-NIRtransmittance or absorbance spectrum, photoluminescence spectra were employed toinvestigate the optical property of6H-SiC neutron irradiated up to1.67×1020n/cm2.The details as follows:1. The defect introduced by neutron irradiation up to1.67×1020n/cm2is mainlypoint defects and its aggregates.2. Irradiation results the increase of absorption and the Urbach energy, the narrowof band gap and the redshift of band edge. Urbach energy decreases along with theincrease of annealing temperature. Urbach energy originate from the transitionbetween the different energy state of band tail.3. New absorption peaks at1178,1410and1710nm are observed in theabsorption spectra. The1178and1410nm peaks are attributed to the siliconvacancies.4. The samples neutron irradiated and post-irradiation annealed below1000°Chave no PL peaks. However, after thermal treatment at1200°C, the510nm,540nm,and575nm peaks are observed. The neutron irradiation leads to the increase ofthreshold wavelength from393nm to1726nm. The threshold wavelength decreaseswith increasing annealing temperature and recovers after1600°C thermal treatment.The luminescence signal can be detected if the threshold wavelength is less than theemission peak wavelength.5. There are two annealing stages in the reply of the SiC crystal. When theannealing temperature is below800℃, most of the point defects, such as Frankel pairs, Si interstitial, C interstitial and C vacancy, disappear. When the annealing temperatureis above800℃, the defect complexes containing silicon vacancies decomposed anddisappeared..6. A new model of“Beryllium-like atom model”is established, to explain thedifferent charge states and related electron transitions of silicon vacancies in SiCcrystal.