表面氧钝化碳化硅纳米团簇电子结构和光学性质的第一性原理研究

基于密度泛函理论(DFT)和广义梯度近似(GGA),对氧钝化条件下4H-SiC纳米团簇的电子结构和光学性质进行了研究。计算了不同直径的4H-SiC纳米球氧钝化后的能带结构、电子态密度和光学性质。团簇的尺度在0.4~0.9 nm之间,构建表面仅存在硅氧双键和表面仅存在碳氧双键的两种模型。研究表明硅氧双键和碳氧双键所引起的缺陷态位于原4H-SiC的价带和导带之间,并且缺陷态与价带顶的能量差随纳米团簇颗粒直径的增大而减小;缺陷态主要是由Si原子外层电子和氧原子外层电子轨道杂化引起的。同时,由于氧的存在,对碳化硅的结构产生一定的影响,这也是缺陷态形成的一个原因。另外,碳氧双键和硅氧双键钝化对4H-SiC纳米团簇的光学性质有着不同的影响。在表面仅存在C=O的情况下,4H-SiC纳米团簇表现出各向同性的性质。在表面仅存在Si=O的情况下,4H-SiC纳米团簇表现出各向异性的性质。

First-principles Calculations of the Electronic Structures and Optical Properties of Oxygen Passivated 4H-SiC Nanostructures

The electronic structures and optical properties of silicon carbide nanoclusters passivation with oxygen atoms have been calculated using density functional theory(DFT).The nanoclusters are obtained from bulk 4H crystal and the energy gaps and optical constants of spherical SiC nanoclusters with different diameters(0.4~0.9 nm) have been calculated.Two models have been constructed,one with only Si=O on the surface and the other one with only C=O on the surface.After oxidization,new localized trap states have been found,which are caused by C=O double bonds and Si=O double bonds based on the band structure and density of states of the clusters.The new trap states are mainly due to the orbital hybridization from the outer electrons of the oxygen and silicon atoms.Meantime,oxygen atoms have effect in some degree on the structures of the nanoclusters,which is another reason for the formation of the localized trap states.Optical constans of nanoclusters have been obtained and analyzed.The calculated results indicate that 4H-SiC nanoclusters exhibit isotropic and anisotropic properties with C=O and Si=O on the surface respectively.