Fe-N共掺杂锐钛矿相TiO_2电子性质与光学性质的第一性原理研究

First-principles study of electronic and optical property of Fe-N co-doped anatase TiO_2

近年来,Fe和N掺杂锐钛矿相TiO_2半导体在实验中发现许多优异性能,本文采用基于密度泛函理论的平面波超软赝势方法研究了纯锐钛矿相TiO_2、Fe和N单掺杂及Fe和N共掺杂TiO_2的能带结构、电荷布居、态密度和光学性质.分析发现:Fe掺杂引起杂质能带位于禁带中央,杂质能带最高点与导带相距大约0.6 eV而最低点与价带相距大约0.2 eV;N掺杂引起的杂质能带位于价带顶部附近.Fe和N共掺杂后杂质能带由两部分组成,位于价带顶上方0.62 eV和导带底下方0.22 eV处,其中一层杂质能带主要由N原子的2p轨道和Fe原子的3d轨道杂化形成,而另一条杂质能带主要由Fe原子的3d轨道形成,由于杂质能级的出现,使锐钛矿TiO_2的禁带宽度变小.对光学性质分析发现:Fe和N共掺杂会使锐钛矿TiO_2光学吸收带边红移,可见光区的光吸收系数明显增大,在低能区出现了新的吸收峰,对应能量为1.82 eV,与实验结果相符.

Many extraordinary characteristics were discovered in Fe and N doped TiO2 in recent years. In this paper, the band structures, density of states, charge population and optical properties of pure, Fedoped, N-doped and Fe-N co-doped anatase-phase TiO2 were studied by using the plane-wave ultrasoft pseudopotentials method based on the density functional theory. The analysis from the band structures, density of states and optical properties showed that three impurity bands located in the middle of band gap in Fe-doped TiO2, in which the top of impurity band was apart from the conduction band by 0. 6 eV and the bottom of the impurity band was at a distance of 0.2 eV from valence band. The N-doped TiO2 produces a new band near the top of valance band. The Fe-N co-doping results in two layers energy bands in the forbidden band gap. One layer impurity band is formed mainly by the N-atom 2p orbital and the Fe-atom 3d orbital hybridized together, the other impurity band mainly is composed of the Fe-atom 3d orbital. Because of the emergence of impurity level, the band gap becomes smaller. It is theoretically predicted that Fe-N co-doped anatase-phase TiOz would lead to the red shift of absorption wavelength and to the increase in coefficient of light absorption. A new absorption peak in the low-energy region,corresponding to energy 1.82 eV, has been found experimentally in Fe-N co-doped anatase-phase TiO2. The present theoretical conclusion is in agreement with the experimental result.