La-N、Gd-N摻雜量對(duì)ZnO電子結(jié)構(gòu)及吸收光譜影響的研究
發(fā)布時(shí)間：2019-06-15 03:23
【摘要】：Zn O因其無(wú)毒、廉價(jià)、穩(wěn)定性好等特點(diǎn),在工業(yè)上得到廣泛應(yīng)用。氧化鋅(Zn O)作為直接禁帶半導(dǎo)體材料,室溫下禁帶寬度為3.37e V,激子束縛能為60me V,具有很好的化學(xué)穩(wěn)定性,在光電材料方面一直受到國(guó)內(nèi)外學(xué)術(shù)界的廣泛關(guān)注。稀土元素具有豐富的電子組態(tài),近年來(lái)其在半導(dǎo)體材料改性的研究中越來(lái)越受到關(guān)注。稀土元素單摻雜或與非金屬共摻雜Zn O將會(huì)顯著改變Zn O的電子結(jié)構(gòu)和光學(xué)性質(zhì),從而影響其光催化性能。本文基于第一性原理,應(yīng)用CASTEP(MS6.0)軟件包中的密度泛函理論(DFT),廣義梯度近似(GGA)下的平面波超軟贗勢(shì)方法(USP),建立了N/La分別單摻雜以及La-N、Gd-N共摻雜Zn O的模型,對(duì)各個(gè)模型進(jìn)行幾何優(yōu)化后計(jì)算了每個(gè)模型的形成能,能帶分布,總態(tài)密度,分態(tài)密度,電子密度與吸收光譜。計(jì)算結(jié)果發(fā)現(xiàn),La、Gd、N分別單摻雜Zn O都在Zn O的禁帶區(qū)域產(chǎn)生雜質(zhì)能級(jí),La、Gd摻雜產(chǎn)生的雜質(zhì)能級(jí)位于禁帶中間區(qū)域,N摻雜產(chǎn)生的雜質(zhì)能級(jí)位于價(jià)帶頂且與價(jià)帶發(fā)生簡(jiǎn)并。態(tài)密度分析表明:施主與受主能級(jí)分別由La、Gd的4f態(tài)和N的2p態(tài)貢獻(xiàn)。隨La、Gd摻雜濃度的提高,施主能級(jí)向深能級(jí)方向移動(dòng),同時(shí)Zn O禁帶寬度略微變窄。隨N摻雜濃度的提高,受主能級(jí)變化不明顯,但禁帶寬度變窄。La-N、Gd-N共摻雜時(shí),產(chǎn)生兩部分雜質(zhì)能級(jí),分別由La、Gd的4f態(tài)和N的2p態(tài)貢獻(xiàn)。與單摻雜情況比較,受主能級(jí)與價(jià)帶簡(jiǎn)并化更明顯,施主能級(jí)略微向淺能級(jí)移動(dòng),但仍處于禁帶中間區(qū)域,淺移化趨勢(shì)不明顯。共摻雜濃度的提高使得施主能級(jí)向深能級(jí)移動(dòng),禁帶寬度進(jìn)一步變窄。結(jié)果表明:La、Gd、N分別單摻雜以及La-N、Gd-N共摻雜Zn O都使得吸收光譜發(fā)生紅移,其中共摻雜的紅移效果最好。通過(guò)形成能計(jì)算發(fā)現(xiàn),共摻雜需要更多的能量,但摻雜體系形成后總能量低于單摻雜體系總能量,即結(jié)構(gòu)相對(duì)穩(wěn)定。對(duì)電子結(jié)構(gòu)的分析發(fā)現(xiàn)共摻雜時(shí),La-N、Gd-N間的吸引力使得La Zn、Gd-Zn與N-O間的排斥力都減小,從而兩部分雜質(zhì)能級(jí)相對(duì)于單摻雜的情況都向淺能級(jí)轉(zhuǎn)化,亦即載流子壽命提高。另一方面施主與受主能級(jí)分別成為電子和空穴的捕獲阱,使得電子空穴更不易復(fù)合而進(jìn)一步提高了載流子壽命。這種La-N、Gd-N共摻雜的協(xié)同效應(yīng)使得Zn O的光催化性能增強(qiáng)。然而摻雜濃度的提高,雖然能使吸收光譜紅移更強(qiáng),卻使得雜質(zhì)能級(jí)向深能級(jí)方向移動(dòng),根據(jù)半導(dǎo)體理論,深能級(jí)是有效的復(fù)合中心,這不利于載流子向表面的傳遞,降低了載流子壽命。綜上所述,La-N、Gd-N共摻雜制備的Zn O光催化劑優(yōu)于La、Gd、N單摻雜制備的Zn O光催化劑。然而,用La-N、Gd-N共摻雜Zn O制備光催化材料時(shí),還需摻雜適量的濃度,做到電子壽命與紅移效應(yīng)二者兼顧。由于稀土La、Gd特殊的電子結(jié)構(gòu),使得其4f態(tài)電子受到外層電子的屏蔽作用,減弱了4f態(tài)電子與其它態(tài)電子的交互雜化作用,因此La-N、Gd-N共摻雜時(shí)施主能級(jí)因協(xié)同效應(yīng)產(chǎn)生的淺移化趨勢(shì)不明顯。
[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，
本文編號(hào)：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，
本文編號(hào)：2499928
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