应变工程中Bi(111)薄膜的半导体-半金属转变及其机理
收稿日期: 2021-05-26
修回日期: 2021-09-15
网络出版日期: 2021-10-15
基金资助
国家自然科学基金项目(61971116)
Strain-Engineered Semiconductor to Semimetallic Transition and Its Mechanism in Bi(111) Film
Received date: 2021-05-26
Revised date: 2021-09-15
Online published: 2021-10-15
Supported by
National Natural Science Foundation of China(61971116)
基于第一性原理,系统研究了不同层数Bi(111)薄膜的几何结构和能带性质,以及双轴应变对Bi(111)薄膜结构与电学性能的调控作用。研究结果表明：Bi(111)薄膜的几何结构以及能带性质具有厚度依赖性。随着厚度的增加,薄膜晶格常数增大,屈曲高度降低,表面能增加,带隙减小,并在3个双层时由半导体性质转变为半金属性质；对1个双层Bi(111)薄膜施加拉伸应变,可诱发间接带隙到直接带隙的转变以及能带反转；施加压缩应变可诱发半导体到半金属性质的转变,通过近带边电子轨道的成键性质分析,揭示了成键态和反键态对应变的不同响应速率,引起了导带底的转移,从而导致了半导体到半金属转变。类似的半导体到半金属转变也可在应变作用下的2~5个双层厚Bi(111)薄膜中预测到。应变也可调节Bi(111)薄膜的电子和空穴的有效质量,从而可能影响薄膜传输特性。
任师浩 , 刘永利 , 孟凡顺 , 祁阳 . 应变工程中Bi(111)薄膜的半导体-半金属转变及其机理[J]. 金属学报, 2022 , 58(7) : 911 -920 . DOI: 10.11900/0412.1961.2021.00225
Bi is a key semimetallic element with strong spin-orbit coupling characteristics, long Fermi wavelengths, quantum size effects, and competitive structural phases. Its spin-orbit coupling can induce the metal surface state of Bi thin film, which is completely different from its bulk properties, indicating that thin Bi film has important research significance in the control of the transmission performance of semiconductor sensors. The biaxial strain deformation and film thickness can induce the transition from semiconductors to semimetals and changes in topological properties. However, the current critical transition thickness obtained using different methods is contentious, and the inherent transition mechanism remains unclear. In this work, the effect and affecting mechanism of biaxial strain on the geometric and band structures of Bi thin films with different thicknesses of Bi thin films were systematically studied and discussed using a first-principles method based on density functional theories. The results show that the band and geometric structures of Bi(111) films are strongly correlated to the thickness. With the increase in the number of atomic layers, the lattice constant increases, the buckling height decreases, the surface energy increases, and the energy bandgap decreases, where a transition of the films from semiconductor to semimetal occurs at the critical thickness of three bilayers (BLs). The application of tensile strain to the one-BL Bi film can induce the transition of energy bandgap from indirect to direct semiconductor accompanied with a band inversion, whereas the compressive strain can induce the transition from semiconductor to semimetal. The analysis of the bond nature of the near-band-edge electronic orbitals revealed that the transition of the semiconductor to the semimetallic state originates from the transition of the conduction band minimum induced by the different response rates of the bonding and antibonding states of the band edge electrons to the strain. A similar transition can be observed for 2-5 Bi BL films under biaxial deformation. The strain deformation can also improve the transport property of Bi films by changing the effective mass of electrons and holes. These findings provide a theoretical insight to regulating the electronic properties of Bi film integrated electronic devices using the strain field.
Key words： Bi film; strain; energy band structure; first-principle method
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