第一性原理研究厚度和空位缺陷对Si/SiO2界面电子结构与光学性质的影响

采用基于密度泛函理论的平面波超软赝势方法，在局域密度近似（ LDA）下研究了Si纳米层厚度和O空位缺陷对Si／SiO2界面电子结构及光学性质的影响．电子结构计算结果表明：在0.815～2.580nm的Si层厚度范围内， Si／SiO2界面结构的能隙随着厚度减小而逐渐增大，表现出明显的量子尺寸效应，这与实验以及其他理论计算结果一致；三种不同的O空位缺陷的存在均使得Si／SiO2界面能隙中出现了缺陷态，费米能级向高能量方向移动，且带隙有微弱增加．光学性质计算结果表明：随着Si纳米层厚度的减小， Si／SiO2界面吸收系数产生了蓝移； O空位缺陷引入后，界面光学性质的变化主要集中在低能区，即低能区的吸收系数和光电导率显著增加．可见，改变厚度和引入缺陷能够有效地调控Si／SiO2界面体系的电子和光学性质，上述研究结果为Si／SiO2界面材料的设计与应用提供了一定的理论依据．

First-principles study of the impact of thickness and vacancy defects on the electronic structure and optical properties of the Si/SiO2 interface

The effects of Si nanolayer thickness and O vacancy defects on the electronic structure and optical properties of Si/SiO2 interface were investigated by first-principles calculations based on density functional theory with the localized density approximation (LDA). The calculated results of the electronic structures indicate that the energy gap of Si/SiO2 interface structure decreases as the thickness increases in the range of 0.815~2.580nm for Si layer thickness, showing obvious quantum size effect, which is consistent with experimental and other theoretical calculation results. The defect states are found all in the band gap of Si/SiO2 interface due to the presences of three different O vacancy defects. At the same time, it is found that Fermi level shifts to the higher energy direction and the band gap increases weakly. The calculated results of the optical properties show that the blue shift of the optical absorption edge is observed in the absorption spectra of Si/SiO2 interface with the decrease of Si nanolayer thickness. After the introduction of O vacancy defects, the changes in the optical properties of the interface are mainly concentrated in the low-energy region, namely a significant increase in the absorption coefficient and optical conductivity in the low energy region. Therefore, changing the thickness and introducing the defects can effectively regulate the electronic and optical properties of the Si/SiO2 interface system. The results of the study provide a theoretical basis for design and application of Si/SiO2 interface nanomaterials.