本文主要研究内容
作者范永军（2019）在《钒铈共掺杂铌酸锂晶体中的极化子及电荷迁移机制研究》一文中研究指出：铌酸锂是一种传统的多功能效应晶体材料,具有优异的压电、铁电、电光、声光及光折变等特性,在压电传感器、激光调制器、表面声波器件等方面得到广泛应用,成为少数经久不衰并不断开发新功能特性和应用领域的重要材料。光致吸收性质是铌酸锂晶体重要的光电特性之一,光致吸收是指激发光入射到晶体上,将陷阱能级上的电子或空穴载流子激发到导带,这些被激发的电子或空穴载流子落到能级上会造成准稳态能级上可以被激发的电子或空穴数目增加,从宏观上导致了某个波段吸收系数的增加。由于极化子是载流子迁移的载体,光致吸收现象通常与晶体中的极化子性质密切相关。同成分铌酸锂晶体中存在多种本征极化子,如铌自由小极化子、反位铌(NbLi)束缚小极化子和双极化子等多种电子极化子。变价金属离子掺杂进入铌酸锂晶格后,通常也能够捕获载流子形成极化子。这些极化子在捕获电子或者空穴的同时伴随较大的晶格畸变,并在带隙中引入陷阱能级。同时,外部掺杂极化子与本征极化子发生相互作用,能够影响带隙中陷阱能级的分布和载流子的迁移过程,进而影响晶体的光致吸收性质。因此,深刻理解电荷被极化子束缚和跃迁的行为以及电荷在陷阱能级之间的跃迁和迁移过程,对于深入了解晶体的光致吸收特性本质是非常重要的,对发展铌酸锂晶体诸多应用具有非常重要的意义。通常情况下,铌酸锂晶体中的外部掺杂极化子多为低价态掺杂离子,如Fe,而高价态金属离子掺杂引起的极化子行为研究则较少。高价态金属离子通常具有多种可变价态,更容易捕获多个电子形成电子极化子,且电子占据轨道的形式和能量也易发生变化,从而产生有趣的光学性质。钒(V)与Nb均为第五副族过渡金属,+5价,其掺杂进入铌酸锂晶格后和本征反位铌NbLi相比,是否具有类似的晶格占位、电子结构、极化子行为等,引起了我们的研究兴趣,是本论文研究的内容之一。此外,铈(Ce)可以与多种过渡金属离子实现共掺,在铌酸锂带隙中引入深浅不一的陷阱能级,这对于调控晶体对不同波长光的吸收和由此导致的电子的跃迁和迁移是非常重要的。因此,我们围绕钒、铈单掺杂和共掺杂铌酸锂晶体中的极化子以及电荷迁移机制开展研究,探讨其在带隙中引入的陷阱能级之间的深浅关系,获得极化子对电子的束缚行为,以及外部掺杂极化子与本征极化子的相互作用机理,进而分析电荷在钒铈掺杂铌酸锂晶体中的迁移机制,这将有助于理解掺杂LiNbO3晶体光学性质的来源。本论文基于第一性原理方法,针对钒、铈单掺杂以及二者共掺杂开展了系统的理论研究工作,研究它们在带隙中引入的陷阱能级性质、极化子的存在形式、结构及其捕获载流子的行为,探讨钒、铈掺杂对铌酸锂晶体光学性质的影响,揭示钒、铈掺杂铌酸锂晶体的电荷迁移机制。主要研究内容及结果如下:第一章绪论部分,主要介绍本论文的研究背景和意义。首先介绍了掺杂LiNb03晶体的应用研究进展和意义,然后详细阐述了LiNb03晶体中极化子以及电荷迁移的研究意义及现状,最后阐明本论文的选题意义和研究思路。第二章理论研究方法部分,详细介绍了密度泛函理论的基本原理、交换相关泛函及自洽场计算流程,并在此基础上介绍了本论文计算所使用的VASP量化软件包。第三章,采用密度泛函理论研究了钒单掺杂铌酸锂的极化子行为,详细探讨了钒掺入铌酸锂中的稳定存在形式、弛豫结构、载流子捕获行为、在带隙中引入的陷阱能级特征等。研究表明,由于晶体中含有大量本征缺陷锂空位(VacLi),费米能级位于价带顶附近,当钒掺杂进入同成分铌酸锂晶体中时优先占据锂格点,形成钒取代锂(VLi)缺陷,并以+4价稳定存在,随着锂空位浓度降低,费米能级向带隙中间移动,+4价VLi缺陷能够同时捕获两个电子形成+2价缺陷,产生负U效应,同时钒开始占据铌格点形成钒取代铌(VNb)缺陷,并以中性态稳定存在;而当V掺杂进入SLN晶体中时,费米能级位于带隙中间,随着V掺杂浓度的增加,费米能级会向导带底方向移动,此时钒能够占据铌格点,并捕获电子发生从0价到-2价的缺陷价态转变。VLi缺陷捕获的两个电子均局域在VLi缺陷中心周围,只引起了最近邻氧八面体的膨胀,是典型的束缚小极化子,VLi继续捕获两个电子,形成中性VLi缺陷时也观察到了类似的束缚小极化子行为。与本征NbLi双极化子相比,由于小极化子的电子束缚能力相对较弱,被束缚的电子更易激发,进而导致电子—空穴复合所需的时间较短,因此对光的响应时间也较短,这与实验上观测到的现象是一致的,从而从微观角度为LiNbO3晶体的实际应用提供理论依据。第四章,进一步研究了钒与本征缺陷反位铌NbLi和锂空位VacLi的相互作用。研究表明,当VLi和NbLi共存于铌酸锂晶格中时,电子首先会被VLi小极化子束缚,分布于VLi和沿非极化方向近邻的Nb离子周围形成束缚双极化子;进一步捕获电子后,VLi与极化方向和非极化方向近邻的Nb离子均产生相互作用,并且均观察到双极化子行为。由此得出,VLi对电子的捕获能力要强于本征缺陷NbLi。此外,VLi极化子在CLN和SLN晶体中的存在形式是不同的,不同的极化子带来了陷阱能级深浅的变化以及电子束缚能力强弱的不同。由于电子从VLi小极化子转移到NbLi双极化子需要的时间较长,因此,V在SLN晶体中掺杂会具有更短的响应时间。在此基础上,我们进一步研究了钒与本征缺陷相互作用形成缺陷团簇的结构和性质。依据实验报道,我们构建了VLi4++NbLi4++8VacLi-、VLi4++4VacLi-VLi4++VNb0+4VacLi-三种电中性的缺陷团簇模型,以体现钒掺杂浓度从低到高的变化。通过构建一系列可能的团簇构型并进行形成能的研究,最终得到了最稳定的团簇结构,缺陷团簇尺寸约2 nm,仍然保持C3对称性。电子结构分析表明,形成缺陷团簇对钒陷阱能级的影响很小,但是对导带底电子态贡献影响很大,尤其是对包含有NbLi和VNb的缺陷团簇而言,会在导带底引入d电子态,从而引起电子跃迁和光学性质的变化。第五章,研究了铈在铌酸锂晶体中的掺杂行为以及钒铈共掺杂铌酸锂的电荷迁移机制,系统分析了掺杂的晶体结构变化、载流子捕获行为、在带隙中引入的陷阱能级等。研究发现,铈优先取代锂格点并以+3价稳定存在,+3价CeLi缺陷能够捕获一个电子形成+2价缺陷,同时伴随着铈占据铌格点,形成-1价缺陷。CeLi3+在带隙中引入的缺陷能级主要由Ce的4f轨道贡献,属于浅能级,捕获一个电子后形成束缚小极化子。当VLi和CeLi共存于铌酸锂晶格中时,二者相互排斥,趋向分离,捕获两个电子后,电子主要局域在VLi缺陷中心周围,以小极化子的形式存在。与V单掺杂相比,钒铈共掺均取代Li位点时,VLi在带隙中引入深能级,CeLi引入浅能级,在两种不同能量的光辐照下,能量较高的光可以激发深能级的电子跃迁到导带或者浅能级,浅能级的电子在能量较低的光的作用下也可以被激发跃迁到导带;在导带中迁移的电子最终被深陷阱中心所捕获,进而引起电子跃迁和光学性质的变化。当VLi和CeNb共存时,同样在带隙中引入深浅不一的陷阱能级,CeNb的弛豫导致VLi陷阱能级向导带方向移动,并且Ce的能级变浅,进而引起的光吸收和电子跃迁与占据Li格点的情况有所差异。最后,综合考虑钒、铈掺杂以及本征缺陷在带隙中引入的缺陷能级,我们对电荷在钒铈共掺杂LiNbO3晶体中的电荷迁移机制进行了详细的分析讨论。第六章,总结归纳本论文的主要结论和创新点,并对下一步拟开展的工作进行了展望。
Abstract
ni suan li shi yi chong chuan tong de duo gong neng xiao ying jing ti cai liao ,ju you you yi de ya dian 、tie dian 、dian guang 、sheng guang ji guang she bian deng te xing ,zai ya dian chuan gan qi 、ji guang diao zhi qi 、biao mian sheng bo qi jian deng fang mian de dao an fan ying yong ,cheng wei shao shu jing jiu bu cui bing bu duan kai fa xin gong neng te xing he ying yong ling yu de chong yao cai liao 。guang zhi xi shou xing zhi shi ni suan li jing ti chong yao de guang dian te xing zhi yi ,guang zhi xi shou shi zhi ji fa guang ru she dao jing ti shang ,jiang xian jing neng ji shang de dian zi huo kong xue zai liu zi ji fa dao dao dai ,zhe xie bei ji fa de dian zi huo kong xue zai liu zi la dao neng ji shang hui zao cheng zhun wen tai neng ji shang ke yi bei ji fa de dian zi huo kong xue shu mu zeng jia ,cong hong guan shang dao zhi le mou ge bo duan xi shou ji shu de zeng jia 。you yu ji hua zi shi zai liu zi qian yi de zai ti ,guang zhi xi shou xian xiang tong chang yu jing ti zhong de ji hua zi xing zhi mi qie xiang guan 。tong cheng fen ni suan li jing ti zhong cun zai duo chong ben zheng ji hua zi ,ru ni zi you xiao ji hua zi 、fan wei ni (NbLi)shu fu xiao ji hua zi he shuang ji hua zi deng duo chong dian zi ji hua zi 。bian jia jin shu li zi can za jin ru ni suan li jing ge hou ,tong chang ye neng gou bu huo zai liu zi xing cheng ji hua zi 。zhe xie ji hua zi zai bu huo dian zi huo zhe kong xue de tong shi ban sui jiao da de jing ge ji bian ,bing zai dai xi zhong yin ru xian jing neng ji 。tong shi ,wai bu can za ji hua zi yu ben zheng ji hua zi fa sheng xiang hu zuo yong ,neng gou ying xiang dai xi zhong xian jing neng ji de fen bu he zai liu zi de qian yi guo cheng ,jin er ying xiang jing ti de guang zhi xi shou xing zhi 。yin ci ,shen ke li jie dian he bei ji hua zi shu fu he yue qian de hang wei yi ji dian he zai xian jing neng ji zhi jian de yue qian he qian yi guo cheng ,dui yu shen ru le jie jing ti de guang zhi xi shou te xing ben zhi shi fei chang chong yao de ,dui fa zhan ni suan li jing ti zhu duo ying yong ju you fei chang chong yao de yi yi 。tong chang qing kuang xia ,ni suan li jing ti zhong de wai bu can za ji hua zi duo wei di jia tai can za li zi ,ru Fe,er gao jia tai jin shu li zi can za yin qi de ji hua zi hang wei yan jiu ze jiao shao 。gao jia tai jin shu li zi tong chang ju you duo chong ke bian jia tai ,geng rong yi bu huo duo ge dian zi xing cheng dian zi ji hua zi ,ju dian zi zhan ju gui dao de xing shi he neng liang ye yi fa sheng bian hua ,cong er chan sheng you qu de guang xue xing zhi 。fan (V)yu Nbjun wei di wu fu zu guo du jin shu ,+5jia ,ji can za jin ru ni suan li jing ge hou he ben zheng fan wei ni NbLixiang bi ,shi fou ju you lei shi de jing ge zhan wei 、dian zi jie gou 、ji hua zi hang wei deng ,yin qi le wo men de yan jiu xing qu ,shi ben lun wen yan jiu de nei rong zhi yi 。ci wai ,shi (Ce)ke yi yu duo chong guo du jin shu li zi shi xian gong can ,zai ni suan li dai xi zhong yin ru shen jian bu yi de xian jing neng ji ,zhe dui yu diao kong jing ti dui bu tong bo chang guang de xi shou he you ci dao zhi de dian zi de yue qian he qian yi shi fei chang chong yao de 。yin ci ,wo men wei rao fan 、shi chan can za he gong can za ni suan li jing ti zhong de ji hua zi yi ji dian he qian yi ji zhi kai zhan yan jiu ,tan tao ji zai dai xi zhong yin ru de xian jing neng ji zhi jian de shen jian guan ji ,huo de ji hua zi dui dian zi de shu fu hang wei ,yi ji wai bu can za ji hua zi yu ben zheng ji hua zi de xiang hu zuo yong ji li ,jin er fen xi dian he zai fan shi can za ni suan li jing ti zhong de qian yi ji zhi ,zhe jiang you zhu yu li jie can za LiNbO3jing ti guang xue xing zhi de lai yuan 。ben lun wen ji yu di yi xing yuan li fang fa ,zhen dui fan 、shi chan can za yi ji er zhe gong can za kai zhan le ji tong de li lun yan jiu gong zuo ,yan jiu ta men zai dai xi zhong yin ru de xian jing neng ji xing zhi 、ji hua zi de cun zai xing shi 、jie gou ji ji bu huo zai liu zi de hang wei ,tan tao fan 、shi can za dui ni suan li jing ti guang xue xing zhi de ying xiang ,jie shi fan 、shi can za ni suan li jing ti de dian he qian yi ji zhi 。zhu yao yan jiu nei rong ji jie guo ru xia :di yi zhang xu lun bu fen ,zhu yao jie shao ben lun wen de yan jiu bei jing he yi yi 。shou xian jie shao le can za LiNb03jing ti de ying yong yan jiu jin zhan he yi yi ,ran hou xiang xi chan shu le LiNb03jing ti zhong ji hua zi yi ji dian he qian yi de yan jiu yi yi ji xian zhuang ,zui hou chan ming ben lun wen de shua ti yi yi he yan jiu sai lu 。di er zhang li lun yan jiu fang fa bu fen ,xiang xi jie shao le mi du fan han li lun de ji ben yuan li 、jiao huan xiang guan fan han ji zi qia chang ji suan liu cheng ,bing zai ci ji chu shang jie shao le ben lun wen ji suan suo shi yong de VASPliang hua ruan jian bao 。di san zhang ,cai yong mi du fan han li lun yan jiu le fan chan can za ni suan li de ji hua zi hang wei ,xiang xi tan tao le fan can ru ni suan li zhong de wen ding cun zai xing shi 、chi yu jie gou 、zai liu zi bu huo hang wei 、zai dai xi zhong yin ru de xian jing neng ji te zheng deng 。yan jiu biao ming ,you yu jing ti zhong han you da liang ben zheng que xian li kong wei (VacLi),fei mi neng ji wei yu jia dai ding fu jin ,dang fan can za jin ru tong cheng fen ni suan li jing ti zhong shi you xian zhan ju li ge dian ,xing cheng fan qu dai li (VLi)que xian ,bing yi +4jia wen ding cun zai ,sui zhao li kong wei nong du jiang di ,fei mi neng ji xiang dai xi zhong jian yi dong ,+4jia VLique xian neng gou tong shi bu huo liang ge dian zi xing cheng +2jia que xian ,chan sheng fu Uxiao ying ,tong shi fan kai shi zhan ju ni ge dian xing cheng fan qu dai ni (VNb)que xian ,bing yi zhong xing tai wen ding cun zai ;er dang Vcan za jin ru SLNjing ti zhong shi ,fei mi neng ji wei yu dai xi zhong jian ,sui zhao Vcan za nong du de zeng jia ,fei mi neng ji hui xiang dao dai de fang xiang yi dong ,ci shi fan neng gou zhan ju ni ge dian ,bing bu huo dian zi fa sheng cong 0jia dao -2jia de que xian jia tai zhuai bian 。VLique xian bu huo de liang ge dian zi jun ju yu zai VLique xian zhong xin zhou wei ,zhi yin qi le zui jin lin yang ba mian ti de peng zhang ,shi dian xing de shu fu xiao ji hua zi ,VLiji xu bu huo liang ge dian zi ,xing cheng zhong xing VLique xian shi ye guan cha dao le lei shi de shu fu xiao ji hua zi hang wei 。yu ben zheng NbLishuang ji hua zi xiang bi ,you yu xiao ji hua zi de dian zi shu fu neng li xiang dui jiao ruo ,bei shu fu de dian zi geng yi ji fa ,jin er dao zhi dian zi —kong xue fu ge suo xu de shi jian jiao duan ,yin ci dui guang de xiang ying shi jian ye jiao duan ,zhe yu shi yan shang guan ce dao de xian xiang shi yi zhi de ,cong er cong wei guan jiao du wei LiNbO3jing ti de shi ji ying yong di gong li lun yi ju 。di si zhang ,jin yi bu yan jiu le fan yu ben zheng que xian fan wei ni NbLihe li kong wei VacLide xiang hu zuo yong 。yan jiu biao ming ,dang VLihe NbLigong cun yu ni suan li jing ge zhong shi ,dian zi shou xian hui bei VLixiao ji hua zi shu fu ,fen bu yu VLihe yan fei ji hua fang xiang jin lin de Nbli zi zhou wei xing cheng shu fu shuang ji hua zi ;jin yi bu bu huo dian zi hou ,VLiyu ji hua fang xiang he fei ji hua fang xiang jin lin de Nbli zi jun chan sheng xiang hu zuo yong ,bing ju jun guan cha dao shuang ji hua zi hang wei 。you ci de chu ,VLidui dian zi de bu huo neng li yao jiang yu ben zheng que xian NbLi。ci wai ,VLiji hua zi zai CLNhe SLNjing ti zhong de cun zai xing shi shi bu tong de ,bu tong de ji hua zi dai lai le xian jing neng ji shen jian de bian hua yi ji dian zi shu fu neng li jiang ruo de bu tong 。you yu dian zi cong VLixiao ji hua zi zhuai yi dao NbLishuang ji hua zi xu yao de shi jian jiao chang ,yin ci ,Vzai SLNjing ti zhong can za hui ju you geng duan de xiang ying shi jian 。zai ci ji chu shang ,wo men jin yi bu yan jiu le fan yu ben zheng que xian xiang hu zuo yong xing cheng que xian tuan cu de jie gou he xing zhi 。yi ju shi yan bao dao ,wo men gou jian le VLi4++NbLi4++8VacLi-、VLi4++4VacLi-VLi4++VNb0+4VacLi-san chong dian zhong xing de que xian tuan cu mo xing ,yi ti xian fan can za nong du cong di dao gao de bian hua 。tong guo gou jian yi ji lie ke neng de tuan cu gou xing bing jin hang xing cheng neng de yan jiu ,zui zhong de dao le zui wen ding de tuan cu jie gou ,que xian tuan cu che cun yao 2 nm,reng ran bao chi C3dui chen xing 。dian zi jie gou fen xi biao ming ,xing cheng que xian tuan cu dui fan xian jing neng ji de ying xiang hen xiao ,dan shi dui dao dai de dian zi tai gong suo ying xiang hen da ,you ji shi dui bao han you NbLihe VNbde que xian tuan cu er yan ,hui zai dao dai de yin ru ddian zi tai ,cong er yin qi dian zi yue qian he guang xue xing zhi de bian hua 。di wu zhang ,yan jiu le shi zai ni suan li jing ti zhong de can za hang wei yi ji fan shi gong can za ni suan li de dian he qian yi ji zhi ,ji tong fen xi le can za de jing ti jie gou bian hua 、zai liu zi bu huo hang wei 、zai dai xi zhong yin ru de xian jing neng ji deng 。yan jiu fa xian ,shi you xian qu dai li ge dian bing yi +3jia wen ding cun zai ,+3jia CeLique xian neng gou bu huo yi ge dian zi xing cheng +2jia que xian ,tong shi ban sui zhao shi zhan ju ni ge dian ,xing cheng -1jia que xian 。CeLi3+zai dai xi zhong yin ru de que xian neng ji zhu yao you Cede 4fgui dao gong suo ,shu yu jian neng ji ,bu huo yi ge dian zi hou xing cheng shu fu xiao ji hua zi 。dang VLihe CeLigong cun yu ni suan li jing ge zhong shi ,er zhe xiang hu pai chi ,qu xiang fen li ,bu huo liang ge dian zi hou ,dian zi zhu yao ju yu zai VLique xian zhong xin zhou wei ,yi xiao ji hua zi de xing shi cun zai 。yu Vchan can za xiang bi ,fan shi gong can jun qu dai Liwei dian shi ,VLizai dai xi zhong yin ru shen neng ji ,CeLiyin ru jian neng ji ,zai liang chong bu tong neng liang de guang fu zhao xia ,neng liang jiao gao de guang ke yi ji fa shen neng ji de dian zi yue qian dao dao dai huo zhe jian neng ji ,jian neng ji de dian zi zai neng liang jiao di de guang de zuo yong xia ye ke yi bei ji fa yue qian dao dao dai ;zai dao dai zhong qian yi de dian zi zui zhong bei shen xian jing zhong xin suo bu huo ,jin er yin qi dian zi yue qian he guang xue xing zhi de bian hua 。dang VLihe CeNbgong cun shi ,tong yang zai dai xi zhong yin ru shen jian bu yi de xian jing neng ji ,CeNbde chi yu dao zhi VLixian jing neng ji xiang dao dai fang xiang yi dong ,bing ju Cede neng ji bian jian ,jin er yin qi de guang xi shou he dian zi yue qian yu zhan ju Lige dian de qing kuang you suo cha yi 。zui hou ,zeng ge kao lv fan 、shi can za yi ji ben zheng que xian zai dai xi zhong yin ru de que xian neng ji ,wo men dui dian he zai fan shi gong can za LiNbO3jing ti zhong de dian he qian yi ji zhi jin hang le xiang xi de fen xi tao lun 。di liu zhang ,zong jie gui na ben lun wen de zhu yao jie lun he chuang xin dian ,bing dui xia yi bu ni kai zhan de gong zuo jin hang le zhan wang 。
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