中子辐照6H-SiC晶体的光学性质及缺陷分析

Optical Properties and Defect Analysis of 6H-SiC Crystals Irradiated by Heavy Neutron

利用透射电子显微镜、紫外--可见--近红外光谱和Raman光谱,对剂量为1.67×1020 n/cm2中子辐照的n型半导体6H-SiC晶体进行了微观结构、光学性质及退火过程的研究。结果显示,辐照并没有造成样品的完全非晶化,辐照缺陷主要是点缺陷及其聚集体。辐照后的样品的光吸收明显增加,带隙变小,Urbach能量变大,且在1 178、1 410和1 710nm处出现新的吸收峰。1 178和1 410nm峰的出现归因于辐照产生的Si空位VSi。对辐照样品进行了室温至1600℃退火,发现800℃是退火过程的转折点。低于800℃退火时,样品中的Frankel对、间隙原子和C空位VC消失;高于800℃退火时,含Si空位VSi缔合缺陷及复杂缺陷团分解湮灭。为了解释与VSi有关的多个光谱峰,建立了SiC中硅空位的"类铍原子模型"。

The microstructure, optical properties and the annealing behavior of N-doped 6 H-SiC crystals irradiated by neutrons at the fluence of 1.67 × 1020 n/cmz were analyzed by transmission electron microscopy （TEM）, UV-VIS-NIR absorption spec- troscopy and Raman spectroscopy, respectively. The results by TEM indicate that the neutron irradiation does not lead to the amorphization. The dominated defects are point defects and their aggregation. After the neutron irradiation, the band gap of 6H-SiC crystal sample becomes narrower, and the Urbach energy and the optical absorption both increase. The absorption peaks at 1 178, 1 410 and I 710 nm appear in the absorption spectra. The peaks at 1 178 and I 410 nm are attributed to the sil- icon vacancies. There is a characteristic temperature of 800 ℃, when the samples are isochronally annealed from room tempera- ture to 1 600℃. When the annealing temperature is〈800 ℃, most of the point defects such as Frankel pairs, Si interstitial, C interstitial and C vacancy disappear. When the annealing temperature is〉800℃, the defect complexes containing silicon va- cancies decompose and disappear. The “Beryllium-like atom model”was proposed to explain the different charge states and the related electron transitions of silicon vacancies in SiC crystal.