La-N、Gd-N掺杂量对ZnO电子结构及吸收光谱影响的研究
发布时间：2019-06-15 03:23
【摘要】：Zn O因其无毒、廉价、稳定性好等特点,在工业上得到广泛应用。氧化锌(Zn O)作为直接禁带半导体材料,室温下禁带宽度为3.37e V,激子束缚能为60me V,具有很好的化学稳定性,在光电材料方面一直受到国内外学术界的广泛关注。稀土元素具有丰富的电子组态,近年来其在半导体材料改性的研究中越来越受到关注。稀土元素单掺杂或与非金属共掺杂Zn O将会显著改变Zn O的电子结构和光学性质,从而影响其光催化性能。本文基于第一性原理,应用CASTEP(MS6.0)软件包中的密度泛函理论(DFT),广义梯度近似(GGA)下的平面波超软赝势方法(USP),建立了N/La分别单掺杂以及La-N、Gd-N共掺杂Zn O的模型,对各个模型进行几何优化后计算了每个模型的形成能,能带分布,总态密度,分态密度,电子密度与吸收光谱。计算结果发现,La、Gd、N分别单掺杂Zn O都在Zn O的禁带区域产生杂质能级,La、Gd掺杂产生的杂质能级位于禁带中间区域,N掺杂产生的杂质能级位于价带顶且与价带发生简并。态密度分析表明:施主与受主能级分别由La、Gd的4f态和N的2p态贡献。随La、Gd掺杂浓度的提高,施主能级向深能级方向移动,同时Zn O禁带宽度略微变窄。随N掺杂浓度的提高,受主能级变化不明显,但禁带宽度变窄。La-N、Gd-N共掺杂时,产生两部分杂质能级,分别由La、Gd的4f态和N的2p态贡献。与单掺杂情况比较,受主能级与价带简并化更明显,施主能级略微向浅能级移动,但仍处于禁带中间区域,浅移化趋势不明显。共掺杂浓度的提高使得施主能级向深能级移动,禁带宽度进一步变窄。结果表明:La、Gd、N分别单掺杂以及La-N、Gd-N共掺杂Zn O都使得吸收光谱发生红移,其中共掺杂的红移效果最好。通过形成能计算发现,共掺杂需要更多的能量,但掺杂体系形成后总能量低于单掺杂体系总能量,即结构相对稳定。对电子结构的分析发现共掺杂时,La-N、Gd-N间的吸引力使得La Zn、Gd-Zn与N-O间的排斥力都减小,从而两部分杂质能级相对于单掺杂的情况都向浅能级转化,亦即载流子寿命提高。另一方面施主与受主能级分别成为电子和空穴的捕获阱,使得电子空穴更不易复合而进一步提高了载流子寿命。这种La-N、Gd-N共掺杂的协同效应使得Zn O的光催化性能增强。然而掺杂浓度的提高,虽然能使吸收光谱红移更强,却使得杂质能级向深能级方向移动,根据半导体理论,深能级是有效的复合中心,这不利于载流子向表面的传递,降低了载流子寿命。综上所述,La-N、Gd-N共掺杂制备的Zn O光催化剂优于La、Gd、N单掺杂制备的Zn O光催化剂。然而,用La-N、Gd-N共掺杂Zn O制备光催化材料时,还需掺杂适量的浓度,做到电子寿命与红移效应二者兼顾。由于稀土La、Gd特殊的电子结构,使得其4f态电子受到外层电子的屏蔽作用,减弱了4f态电子与其它态电子的交互杂化作用,因此La-N、Gd-N共掺杂时施主能级因协同效应产生的浅移化趋势不明显。
[Abstract]:Zn O has been widely used in industry because of its non-toxic, cheap, good stability and so on. Zinc oxide (Zn O) as a direct band gap semiconductor material, the band gap is 3.37e V at room temperature, and the exciton binding energy is 60me V. it has good chemical stability and has been widely concerned by the academic circles at home and abroad in optoelectronic materials. Rare earth elements have rich electronic configurations, which have attracted more and more attention in the study of semiconductor material modification in recent years. Single doping or co-doping of rare earth elements with non-metallic Zn O will significantly change the electronic structure and optical properties of Zn O, thus affecting its photocatalytic performance. In this paper, based on the first principle, the plane wave ultra-soft pseudopotential method (USP), under the generalized gradient approximation of (DFT), in CASTEP (MS6.0) software package is used to establish the models of N/La single doping and La-N,Gd-N co-doping Zn O, respectively. after geometric optimization of each model, the formation energy, band distribution, total density of states and partial density of states of each model are calculated. Electronic density and absorption spectrum. The calculated results show that the impurity energy levels of La,Gd,N are produced in the band gap region of Zn O, the impurity energy levels produced by La,Gd doping are located in the middle region of the band gap, and the impurity energy levels produced by N doping are located at the top of the valence band and degenerated with the valence band. The analysis of state density shows that the donor and recipient energy levels are contributed by the 4f state of La,Gd and the 2p state of N, respectively. With the increase of La,Gd doping concentration, the donor energy level moves to the deep level, and the band gap of Zn O narrows slightly. With the increase of N doping concentration, the main energy level does not change obviously, but the band gap narrows. When La-N,Gd-N co-doping, two parts of impurity energy levels are produced, which are contributed by the 4f state of La,Gd and the 2p state of N, respectively. Compared with the single doping case, the degeneralization of the recipient energy level and the valence band is more obvious, and the donor energy level moves slightly to the shallow energy level, but it is still in the middle of the band gap, and the trend of shallow shift is not obvious. With the increase of co-doping concentration, the donor energy level moves to the deep level, and the band gap is narrowed further. The results show that the red shift of absorption spectrum is caused by single doping of La,Gd,N and co-doping of La-N,Gd-N respectively, and the red shift effect of co-doping is the best. Through the calculation of formation energy, it is found that more energy is needed for co-doping, but the total energy of the doping system is lower than that of the single doping system, that is to say, the structure is relatively stable. The analysis of electronic structure shows that the attraction between La-N,Gd-N decreases the repulsive force between La 鈮，
本文编号：2499928
[Abstract]:Zn O has been widely used in industry because of its non-toxic, cheap, good stability and so on. Zinc oxide (Zn O) as a direct band gap semiconductor material, the band gap is 3.37e V at room temperature, and the exciton binding energy is 60me V. it has good chemical stability and has been widely concerned by the academic circles at home and abroad in optoelectronic materials. Rare earth elements have rich electronic configurations, which have attracted more and more attention in the study of semiconductor material modification in recent years. Single doping or co-doping of rare earth elements with non-metallic Zn O will significantly change the electronic structure and optical properties of Zn O, thus affecting its photocatalytic performance. In this paper, based on the first principle, the plane wave ultra-soft pseudopotential method (USP), under the generalized gradient approximation of (DFT), in CASTEP (MS6.0) software package is used to establish the models of N/La single doping and La-N,Gd-N co-doping Zn O, respectively. after geometric optimization of each model, the formation energy, band distribution, total density of states and partial density of states of each model are calculated. Electronic density and absorption spectrum. The calculated results show that the impurity energy levels of La,Gd,N are produced in the band gap region of Zn O, the impurity energy levels produced by La,Gd doping are located in the middle region of the band gap, and the impurity energy levels produced by N doping are located at the top of the valence band and degenerated with the valence band. The analysis of state density shows that the donor and recipient energy levels are contributed by the 4f state of La,Gd and the 2p state of N, respectively. With the increase of La,Gd doping concentration, the donor energy level moves to the deep level, and the band gap of Zn O narrows slightly. With the increase of N doping concentration, the main energy level does not change obviously, but the band gap narrows. When La-N,Gd-N co-doping, two parts of impurity energy levels are produced, which are contributed by the 4f state of La,Gd and the 2p state of N, respectively. Compared with the single doping case, the degeneralization of the recipient energy level and the valence band is more obvious, and the donor energy level moves slightly to the shallow energy level, but it is still in the middle of the band gap, and the trend of shallow shift is not obvious. With the increase of co-doping concentration, the donor energy level moves to the deep level, and the band gap is narrowed further. The results show that the red shift of absorption spectrum is caused by single doping of La,Gd,N and co-doping of La-N,Gd-N respectively, and the red shift effect of co-doping is the best. Through the calculation of formation energy, it is found that more energy is needed for co-doping, but the total energy of the doping system is lower than that of the single doping system, that is to say, the structure is relatively stable. The analysis of electronic structure shows that the attraction between La-N,Gd-N decreases the repulsive force between La 鈮，
本文编号：2499928
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