Knowledge Management System Of Institute of Semiconductors,CAS
|Place of Conferral||北京|
|Keyword||纳米半导体材料 本征缺陷 掺杂原子 电子性质 磁性 应变 第一性原理计算|
|Other Abstract|| 自从稳定的石墨烯被成功分离出来，像石墨烯这类二维层状材料因其具有极高的载流子迁移率和杨氏模量及自旋输运等奇特的物理性质而引起人们广泛关注。近来，这类二维材料已经应用于催化剂、储能、光学器件和传感电学器件等科学技术领域。为了充分发挥它们的应用前景，研究这类材料制备过程中产生晶格缺陷和结构形变对电子和磁学性质的影响，显得尤为重要。本文主要围绕GaS、TiS3和ReSe2这三种二维层状材料展开深入研究，利用第一性原理方法探究它们内部缺陷和结构形变产生的微观物理性质变化，主要研究内容和结论如下： （i）用密度泛函理论系统研究单层和体材料GaS中镓空位VGa、硫空位VS、镓替代硫GaS、硫替代镓SGa、镓间隙Gai和硫间隙Si这6种本征点缺陷的电子和磁性性质。对单层材料，除Si外，所有缺陷结构的带隙中都存在缺陷能级。在VGa和Gai中，存在半金属性。含有VGa、GaS、SGa和Gai的单层材料及含有VGa、GaS和SGa的体材料总磁矩均为1.0 μB；而含有VS和Si的单层材料及含有Gai的体材料均为自旋非极化。另外，N和P型GaS单层材料分别在富镓和富硫环境下容易得到，GaS和SGa分别为最适宜的N和P型缺陷。（ii）用第一性原理方法系统研究GaS单层材料掺杂12种不同原子的结构、电子和磁性性质。在非金属原子H、B、C、N、O和F及过渡金属原子V、Cr、Mn、Fe、Co和Ni掺杂硫位中，N是最具前景的P型掺杂。无论在富镓还是富硫环境下，过渡金属原子都难以融入GaS单层材料中。非金属原子掺杂的GaS总磁矩为0 μB或1 μB，而过渡金属杂质的磁矩随着由V到Ni价电子数增加而由5 μB减少到0 μB。对于过渡金属掺杂镓位，Cr和Co上自旋态分别距离导带底和价带顶最近。这些杂质掺杂的所有单层材料都存在磁性基态。引入B和Mn占据硫位及V、Fe、Co和Ni占据镓位从一种自旋轨道将GaS单层材料间接带隙调节为直接带隙。（iii）利用第一性原理探讨了体材料和多层TiS3的结构和电子性质以及平面内应力对TiS3单层材料电子性质的影响。对于多层TiS3，带隙随着层数增加而减小，但都是直接带隙半导体，且价带顶和导带底均位于Γ点；TiS3体材料为间接带隙。由体材料和多层TiS3载流子有效质量得到，多层材料比体材料表现出更强烈的各向异性。在弹性形变范围内施加沿a方向单轴应力εa、沿b方向单轴应力εb和双轴应力εu对TiS3单层材料电子性质的影响不同。εa和εu都使TiS3保持直接带隙，应力可以使带隙从0.08 eV到1.89 eV实现连续调节，这使得TiS3成为未来光电器件极具前景的材料。 |
（iv）实验结果表明，在到达断裂极限前，纳米级的局部应力可以调控ReSe2的光学带隙，诱导磁性产生，并且可以改变其电子和磁性性质。理论上，用第一性原理方法解释了ReSe2产生褶皱后带隙减小的实验机理，并证明了褶皱结构产生磁性。; Since the successful isolation of stable graphene, kinds of two dimensional (2D) layered materials have attracted extensive attention due to their exotic physical properties such as extremely high carrier mobilities and Young modulus and spin transport. Recently, these materials have promising applications in various science and technology fields such as catalysts, energy storage, optical device, and sensing electrical device. To develop their application prospect, it is important to research the influence of lattice defect and structural deformation during the preparation on their electronic and magnetic properties. This thesis mainly focuses on 2D layered materials GaS, TiS3, and ReSe2, and their effects of defect and deformation structure on microscopic physical properties using first-principles calculations. The main conclusions are summarized as follow: (i) The electronic and magnetic properties of native point defects, including vacancies (VGa and VS), antisites (GaS and SGa), and interstitials (Gai and Si) in monolayer and bulk GaS, were systemically studied using the density functional theory method. For the monolayer, the impurity states apperared in the band gaps of all defect structures except interstitial Si. Half-metallic behavior can be obtained in the presence of VGa and Gai. Monolayer with VGa, GaS, SGa, and Gai had a total magnetic moment of 1.0 μB, as did the bulk samples with VGa, GaS, and SGa, whereas the monolayers with VS and Si and bulk sample with Gai were spin-unpolarized. In addition, N- and P-type GaS monolayers were obtained under Ga-rich and S-rich conditions, respectively. GaS and SGa were indentified as suitable N- and P-type defects, respectively. (ii) The structural, electronic, and magnetic properties of the GaS monolayer doped by 12 different kinds of atoms were investigated systemically using first-principles calculations. N is found to be the most promising candidate for P-type doping among dopants at the S site, including nonmetal atoms H, B, C, N, O, and F and transition metal atoms V, Cr, Mn, Fe, Co, and Ni. Transition metal atoms appear to be hardly incorporated in the GaS monolayer under either S- or Ga-rich conditions. While the net magnetic moments of doped GaS by nonmetal atoms are either 0 or 1 μB, the value of transition metal dopants decreases from 5 to 0 μB by adding the number of valence electrons from V to Ni. In the case of transition metal dopants at the Ga site, the majority spin states of Cr and Co are located closest to the conduction band minimum and valence band maximum, respectively. Magnetic ground states exist in all of the monolayers doped by these impurities. Indirect band gap of the pristine GaS monolayer is regulated to be direct from one type of spin channel by introducing B and Mn in the S site and V, Fe, Co, and Ni in the Ga site.(iii) The structural and electronic properties of the bulk and few-layer TiS3 and the influence of in-plane strain on the electronic property of TiS3 monolayer are investigated using first-principles methods. For few-layer TiS3, the computed values of direct band gap decrease with increasing number of layer, and their valence band maximum and conduction band minimum are located at Γ point. However, the band gap of TiS3 bulk is indirect. Moreover, stronger anisotropy in few-layer TiS3 compared to bulk in regard to their carrier effective mass. The response of TiS3 to uniaxial strain along a (εa) and b (εb) direction and biaxial strain (εu) is different in the range of elastic deformation. TiS3 always possesses direct band gap with the action of εa and εu. Band gap is regulated by strain ranging from 0.08 eV to 1.89 eV, which offers a promising material for future photoelectric devices.
(iv) Experimentally, the optical band gap of ReSe2 sheet is regulated by nanoscale local strain. Strain can bring magnetical ground state and modulate the electronic and magnetic properties of ReSe2. Theoretically, the reason why band gap of ReSe2 decreases after wrinkle is explained using first-principles calculations, and the fact that wrinkle structure performs magnetic state is verified.
|陈卉. 半导体纳米材料掺杂和应力调控的第一性原理研究[D]. 北京. 中国科学院研究生院,2016.|
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