Li掺杂对4H-SiC光电性质影响的理论研究

Theoretical study on the effect of Li doping on the photoelectric properties of 4H-SiC

采用基于密度泛函理论的第一性原理方法,计算了Li掺杂4H-SiC体系的电子结构及光学性质.结果表明,掺杂前后的4H-SiC均为间接带隙半导体,Li原子间隙掺杂后形成n型半导体,Li原子替位式掺杂体系的禁带中出现了杂质能级,降低了电子跃迁时所需的能量;对电荷差分密度图的分析表明,Li原子失去电子,导致Li-C键和Li-Si键的共价性降低,以离子性为主;在可见光区域,相比于4H-SiC体系,掺杂体系的吸收率峰值均有所提高,其中Li间隙掺杂体系吸收带边最小,吸收率峰值最大,掺杂后的4H-SiC体系对红外、可见光、紫外均能够有所吸收,说明Li掺杂能够有效拓宽4H-SiC对光的响应范围.

The electronic structure and optical properties of Li doped 4H-SiC system are calculated by the first principle method based on density functional theory.The results show that the 4H-SiC before and after doping are indirect bandgap semiconductors,and n-type semiconductors are formed after Li element interstitial doping.Impurity levels appear in the bandgap of Li element substitution doping system,reducing the energy required for electronic transitions.The analysis of the charge differential density plot shows that the loss of electrons in Li atoms leads to a decrease in the covalence of Li-C bonds and Li-Si bonds,mainly ionic.In the visible light region,compared to the 4H-SiC system,the absorption peak of the doped system has been improved.Among them,the Li interstitial doped system has the smallest absorption band edge and the highest absorption peak.The doped 4H-SiC system can absorb infrared,visible,and ultraviolet lights,indicating that Li doping can effectively expand the response range of 4H-SiC to light.