中子辐照半绝缘SiC单晶的光学性质

Optical Properties of Neutron-irradiated Semi-insulating SiC Single Crystals

利用荧光光谱、紫外-可见-近红外透射光谱和Raman光谱对经1.67×1020n/cm2中子辐照的半绝缘SiC的光学性质进行了研究。结果表明:中子未辐照的和辐照后退火温度低于1000℃的样品未出现任何发射峰;1200℃退火的样品在510、540和575nm处出现了3个绿色发射峰,其中,510和540 nm处的发射峰在经过1 600℃退火后依然存在。中子辐照导致SiC的截止波长由393 nm增大到1 726 nm;随退火温度提高,截止波长逐渐减小,并在1600℃退火后完全回复。Raman光谱显示:辐照诱发了许多新的振动模,如187、278、435和538cm-1处的Si—Si键振动模,600、655和709 cm-1处的Si—C键振动模和1419cm-1处C—C键振动模。辐照缺陷引起声子限制效应,表现为FTO2/6和FLO0/6Raman特征峰的不对称性展宽和红移。在低于1000℃退火阶段,主要表现为不对称性展宽和红移逐渐减弱;在高于1000℃退火阶段,主要表现为辐照产生的新Raman峰逐渐消失。

The optical properties of semi-insulating SiC neutron irradiated up to 1.67 ×10^20n/cm2 were analyzed by photoluminescence （PL） spectroscopy, UV-Vis-Nir transmission spectroscopy and Raman spectroscopy, respectively. The samples neutron irradiated and post-irradiation annealed below 1 000 ℃ had no PL peaks. However, the 510, 540 and 575 nm peaks appeared after thermal treatment at 1 200 ℃. The 510 and 540nm peaks could maintain after thermal treatment at 1 600 ℃. The neutron irradiation led to the increase of threshold wavelength from 393 nm to 1 726 nm. The threshold wavelength decreased with increasing annealing tempera- ture, and recovered after thermal treatment at 1 600 ℃. Several additional vibration modes appeared after irradiation. The peaks at 187, 278, 435 and 538 cm-1 were related to Si-Si vibration, the peaks at 600, 655, and 709 cm-l originated from the SiC vibration, and the peak at 1 419 cm-1 arised from the C-C vibration. The phonon confinement effect was also observed for FTO2/6 and FLO0/6 peaks, showing the asymmetric broadening and red shift. The thermal evolution of Raman spectra with annealing temperature was that the asymmetric broadening and red shift was diminished during annealing at 〈 1 000 ℃, but the irradiation-produced additional Raman peaks were removed during annealing at 〉 1 000 ℃.