单层Nb_(2)SiTe_(4)基化合物的带隙异常变化  

Band gap anomaly in single-layer Nb_(2)SiTe_(4)-based compounds

作　　者：王晓菲 孟威威 赵培丽 贾双凤 郑赫 王建波 Wang Xiao-Fei;Meng Wei-Wei;Zhao Pei-Li;Jia Shuang-Feng;Zheng He;Wang Jian-Bo(Institute for Advanced Studies,MOE Key Laboratory of Artificial Micro-and Nano-structures,Center for Electron Microscopy,School of Physics and Technology,Wuhan University,Wuhan 430072,China;Suzhou Institute of Wuhan University,Suzhou 215123,China;Wuhan University Shenzhen Research Institute,Shenzhen 518057,China;Core Facility of Wuhan University,Wuhan 430072,China)

机构地区：[1]武汉大学物理科学与技术学院,电子显微镜中心,人工微结构教育部重点实验室,高等研究院,武汉430072 [2]武汉大学苏州研究院,苏州215123 [3]武汉大学深圳研究院,深圳518057 [4]武汉大学科研公共服务条件平台,武汉430072

出　　处：《物理学报》2023年第5期297-305,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:52071237,12074290,51871169,52101021,12104345);江苏省自然科学基金(批准号:BK20191187);湖北省青年拔尖人才计划;深圳市科创委基础研究面上项目(批准号:JCYJ20190808150407522);中国博士后科学基金(批准号:2019M652685)资助的课题。

摘　　要：传统硫族化合物中阳离子相同时,随着阴离子原子序数的增加,价带顶逐渐升高,带隙呈减小趋势.在A_(2)BX_(4)基(A=V,Nb,Ta;B=Si,Ge,Sn;X=S,Se,Te)化合物中,观察到随着阴离子原子序数增加,其带隙呈现反常增大的现象.为了探究其带隙异常变化的原因,基于第一性原理计算,对A_(2)BX_(4)基化合物的电子结构展开系统地研究,包括能带结构、带边相对位置、轨道间耦合作用以及能带宽度等影响.研究发现,Nb_(2)SiX_(4)基化合物中Nb原子4d轨道能量明显高于阴离子p轨道,其价带顶和导带底主要由Nb原子4d轨道相互作用组成,其带宽主要影响带隙大小.Nb_(2)SiX_(4)基化合物的带隙大小通过Nb—Nb和Nb—X键共同作用于Nb原子4d轨道的宽度来控制.当阴离子序数增加时,Nb—Nb键长增加,其相互作用减弱,由Nb原子4d轨道主导的能带变宽,带隙减小;另一方面,Nb—X键长增加又使Nb原子4d带宽变窄,带隙增加,并且Nb—X键长增长占主导,所以带隙最终呈现异常增加的趋势.Two-dimensional(2D)niobium silicon telluride(Nb_(2)SiTe_(4))with good stability,a narrow band gap of 0.39 eV,high carrier mobility and superior photoresponsivity,is highly desired for applications in mid-infrared(MIR)detections,ambipolar transistors.Intensive investigations on its ferroelasticity,anisotropic carrier transport,anisotropic thermoelectric property,etc.,have been reported recently.Motivated by the above prominent properties and promising applications,we systematically study the electronic properties of single-layer(SL)A_(2)BX_(4) analogues(A=V,Nb,Ta;B=Si,Ge,Si;X=S,Se,Te)and find a band-gap anomaly with respect to anion change,which differs from conventional 2D metal chalcogenide.In conventional binary chalcogenide,when cations are kept fixed,the bandgap tends to decrease as the atomic number of anions in the same group increases.However,in SL A_(2)BX_(4),as atomic number of anions increases,its bandgaps tend to increase,with cations kept fixed.In order to find the underlying mechanism of such an abnormal bandgap,using firstprinciples calculations,we thoroughly investigate the electronic structures of Nb_(2)SiX_(4)(X=S,Se,Te)surving as an example.It is found that the valance band maximum(VBM)and conduction band minimum(CBM)are mainly derived from the bonding and antibonding coupling between Nb 4d states.The bandwidth of Nb 4d states determines the relative value of the band gap in Nb_(2)SiX_(4).We demonstrate that the band gap is largely influenced by the competition effect between Nb—Nb and Nb—X interactions in Nb_(2)SiX_(4).As the anion atomic number increases,the Nb—Nb bond length increases,yielding an increased bandwidth of Nb 4d state and a smaller bandgap of Nb_(2)SiX_(4).Meanwhile,as Nb—X bond length increases,the bandwidth of Nb 4d however decreases,yielding a larger bandgap.The interaction between Nb and X should be dominant and responsible for the overall bandgap increase of Nb_(2)SiX_(4) compared with the Nb—Nb interaction.

关 键 词：Nb_(2)SiTe_(4) 带隙异常 电子结构 第一性原理计算 

分 类 号：O469[理学—凝聚态物理]