Janus Ga₂XY（X,Y=S,Se,Te;X≠Y）及其异质结的第一性原理研究

【作者】 陈蓉；

【导师】 谢泉；

【作者基本信息】 贵州大学 ， 电子信息， 2023， 硕士

【摘要】 众所周知,二维层状半导体材料拥有电学、力学、光学等物理特性,受到电子、物理、化学等领域研究人员的广泛关注。二维材料衍生出的新兴Janus二维材料是一类具有不对称结构的纳米材料,由两个或多个具有不同极性的区域组成,可以整合两种或两种以上的物理化学性质从而产生出许多新颖的特性。Janus二维材料因其独特的结构和优异的性质,已成为当今凝聚态物理学中备受关注的研究方向之一。本文基于密度泛函理论的第一性原理计算研究了二维Janus Ga₂XY（X,Y=S,Se,Te;X≠Y）的结构和电子性质。研究结果表明,Ga₂SSe是一种具有带隙值为2.05 eV的间接带隙半导体,Ga₂STe与Ga₂SeTe是具有带隙值分别为0.90eV和1.22 eV的直接带隙半导体。由于Janus结构破坏了反演对称性,原子间电负性大小的差距会影响Janus材料的偶极矩,计算得出Ga₂STe的偶极矩最大,Ga₂SeTe的偶极矩最小。大量研究者们通过构建异质结对二维材料的性质进行调控与改善,将不同的二维材料以无数种方式堆叠在一起可得到不同性质的二维范德瓦尔斯异质结。范德瓦耳斯异质结不仅能够保留二维材料的原有性能,还会产生出优异的物理化学性质。因此,本文构建了石墨烯/Ga₂SSe、石墨烯/Ga₂STe、锗烯/Ga₂SeTe三种异质结,共形成了六种不同接触界面的结构。分析异质结的结构稳定性发现,S-Gr接触界面的石墨烯/Ga₂SSe异质结具有-155.97 meV/（?）²的结合能,结构相对于其余五种异质结呈现出最稳定性。通过能带结构发现六种异质结都形成了肖特基接触,其中Te-Gr接触界面的石墨烯/Ga₂STe异质结形成p型肖特基接触,其余五种异质结均形成n型肖特基接触,这些计算结果表明三种异质结是设计新型肖特基电子器件的理想材料。此外,六种不同接触界面异质结的能带结构都保留了石墨烯或锗烯的零带隙（狄拉克锥）性质,计算发现这些异质结的有效质量都很低,表明它们都有超高的载流子迁移率,使得它们在高速纳米电子器件的应用领域发挥着重要的作用。本文还研究了异质结界面电学性质,Te-Gr接触界面的石墨烯/Ga₂STe异质结呈现出最大的功函数与偶极矩,Te-Ge接触界面的锗烯/Ga₂SeTe异质结静电势产生的电场方向（Ge→Te）与内建电场方向相同,促进了界面间电荷转移,导致此异质结的电荷转移强度最大。最后,本文还通过改变层间距对石墨烯/Ga₂SSe、石墨烯/Ga₂STe、锗烯/Ga₂SeTe三种异质结的电子结构进行调控,肖特基势垒高度及其接触类型会受到异质结层间距改变的影响。研究发现肖特基接触类型可以从n型过渡到p型肖特基接触,或从肖特基接触过渡到欧姆接触。这些结果为基于石墨烯/Ga₂SSe、石墨烯/Ga₂STe、锗烯/Ga₂SeTe三种异质结的可控肖特基纳米器件的设计提供了理论指导。特别的是,锗烯/Ga₂SeTe异质结的能带结构在狄拉克锥（K点）处产生了微小的带隙,还发现Se-Ge接触界面异质结的带隙随层间距的减小而增大。本文从理论上提供了一种打开锗烯带隙的有效方法,表明TeGa₂Se/Ge异质结在高性能光电器件的研究领域具有重要的学术意义和潜在的应用价值。更多还原

【Abstract】 As we all know,two-dimensional semiconductor materials have physical properties such as electrical,mechanical,and optical properties,and have received extensive attention from researchers in the fields of electronics,physics,and chemistry.The emerging Janus materials derived from two-dimensional materials are a class of nanomaterials with asymmetric structures.It consists of two or more regions of different polarity and can integrate two or more physical and chemical properties to produce many novel properties.Janus material has become one of the research directions of condensed matter physics because of its unique structure and excellent properties.The structure and electronic properties of Janus Ga₂XY（X,Y=S,Se,Te;X≠Y）are studied by first principles calculations based on density functional theory in this paper.The calculation results show that Ga₂SSe is an indirect band gap semiconductor with a band gap value of 2.05 eV,Ga₂STe and Ga₂SeTe are direct band gap semiconductors with band gap values of 0.90 eV and 1.22 eV,respectively.Since the structure of Janus materials destroys the inversion symmetry,the difference in electronegativity between atoms will affect the dipole moment of Janus material.It is calculated that the dipole moment of Ga₂STe is the largest and the dipole moment of Ga₂SeTe is the smallest.A large number of researchers can regulate and improve the properties of two-dimensional materials by constructing heterostructures.Two-dimensional van der Waals heterostructures with different properties can be obtained by stacking different two-dimensional materials in numerous stacking modes.Van der Waals heterostructures can not only retain the original properties of 2D materials,but also produce excellent physical and chemical properties.The six stacking modes of graphene/Ga₂SSe,graphene/Ga₂STe and germanene/Ga₂SeTe heterostructures are constructed.The graphene/Ga₂SSe heterostructure at the S-Gr contact interface has a binding energy of-155.97 meV/（?）²,and the structure is the most stable relative to the other five heterostructures.It is found that all six heterostructures form Schottky contact,the graphene/Ga₂STe heterostructure at Te-Gr contact interface forms p-type Schottky contact,and the other five heterostructures form n-type Schottky contact.These results show that the three heterostructures are ideal materials for designing new Schottky electronic devices.In addition,the band structures of the three heterostructures retain the zero-bandgap（Dirac cone）of graphene or germanene.It is found that the effective mass of these heterostructures is very low,indicating that they have ultra-high carrier mobility,which makes them play an important role in the application of high-speed nanoelectronic devices.We also studied the charge transfer mechanism of heterostructures interface.The graphene/Ga₂STe heterostructure at the Te-Gr contact interface exhibits the largest work function and dipole moment.The electric field direction（Ge→Te）generated by the electrostatic potential of the germanene/Ga₂SeTe heterostructure at the Te-Ge contact interface is the same as the built-in electric field direction,which promotes the charge transfer between the interfaces,resulting in the maximum charge transfer intensity of this heterostructure.Finally,the graphene/Ga₂SSe,graphene/Ga₂STe and germanene/Ga₂SeTe van der Waals heterostructures are regulated by changing the interlayer distances.The research shows that the change of interlayer distances will affect the Schottky barrier height and Schottky contact type of these heterostructures.The Schottky contact type transitions from n-type to p-type Schottky contact or from Schottky contact to ohmic contact.These results provide theoretical guidance for the design of controllable Schottky nanodevices based on graphene/Ga₂SSe,graphene/Ga₂STe and germanene/Ga₂SeTe heterostructures.In particular,the band structure of germanene/Ga₂SeTe heterostructure has a small band gap in the Dirac cone（K point）.It is also found that the band gap value of the Se-Ge contact interface heterostructure increases with the decrease of the interlayer distances.An effective method has been theoretically provide to open the band gap of germanene,indicating that TeGa₂Se/Ge heterostructure has important academic significance and potential application value in the research field of high-performance optoelectronic devices.更多还原