二维材料光电性质改性的第一性原理研究

发布时间：2018-05-17 09:42

本文选题：二维材料 + 密度泛函理论　；参考：《中国科学院大学(中国科学院上海技术物理研究所)》2017年硕士论文

【摘要】：二维材料凭借它非比寻常的物理特性在电学和光电子领域展现出很大的应用潜能。对器件来说,如场效应晶体管,半导体二维材料需要金属接触电极,半导体金属接触往往在界面形成一个肖特基势垒。如何形成低电阻接触是一个挑战,这对于实现高的开电流、大的光响应和高频运行是十分重要的。本文基于密度泛函理论的第一性原理方法研究了二维材料本征特性、掺杂对二维材料电子结构的影响、金属-二维材料接触肖特基势垒以及掺杂对金属-二维材料界面肖特基势垒的影响。具体内容包括:1.利用第一性原理的方法研究了体材料石墨、MoS2、WS2和黑磷的最稳定结构,得到了相应原胞的总能和体材料的晶格常数。2.在优化好体材料石墨、MoS2、WS2和黑磷的原胞晶格常数的基础上,建立相应的单层结构,通过原子弛豫得到了稳定的单层二维材料,分别采用LDA和GGA形式的交换关联能计算了graphene、单层MoS2、单层WS2和单层BP的能带和态密度,研究结果一致表明:graphene是0带隙的半金属,单层MoS2、单层WS2和单层BP均为直接带隙半导体。3.在优化好MoS2晶格常数的基础上建立了3×3×1的单层MoS2超胞,研究了S空位和Mo空位的缺陷形成能,发现S空位的缺陷形成能比Mo空位的小,这说明S空位形式的缺陷更容易形成,这与实验上观察到纯净MoS2表面容易产生S空位的结论是一致的。据此,计算了不同卤族原子替代S原子掺杂的缺陷形成能,发现Ef(F)Ef(I)Ef(Cl)Ef(Br),这说明在单层MoS2中F原子最容易掺杂,Br原子比较难掺入单层MoS2。计算了卤族原子替代S掺杂后稳定结构的能带和态密度,发现卤族元素掺杂使得带隙宽度变大,并在带隙中引入了杂质能级。4.通过固定二维材料的晶格常数,以金属匹配二维材料晶格常数的形式建立了金属-二维材料界面,包括:(1)Mg-graphene、Cu-graphene、Al-graphene、Au-graphene、Pt-graphene,用基于密度泛函理论的第一性原理方法研究了金属对石墨烯费米能级的调制效应,发现Mg、Cu和Al金属对石墨烯的费米能级属于n型调控,而Au和Pt对石墨烯费米能级的调控属于p型调控,计算结果和文献报道是一致的;(2)Mg-MoS2、Al-MoS2、Cu-MoS2、Au-MoS2、Ti-MoS2、Ni-MoS2、Pt-MoS2、Pd-MoS2,研究结果显示Mg、Al、Cu、Au和单层MoS2接触属于n型接触,其中Mg、Al、Cu与单层MoS2接触形成的肖特基势垒高度较低,比较接近欧姆接触,而Au、Ti、Ni、Pt、Pd和单层MoS2接触形成的肖特基势垒高度较高,是典型的肖特基接触;(3)Mg-WS2、Cu-WS2、Al-WS2、Ti-WS2、Au-WS2、Ni-WS2、Pt-WS2、Pd-WS2,其中Mg、Cu、Al与单层WS2接触形成的肖特基势垒高度较低,比较接近欧姆接触,而Au、Ni、Ti、Pt、Pd和单层WS2接触形成的肖特基势垒高度较高,是典型的肖特基接触;(4)Al-BP、Au-BP,结果显示Al和黑磷接触形成的势垒要比Au和黑磷接触形成的势垒低,这说明相比于Au,Al可能是更好的金属电极。5.通过第一性原理方法研究了卤族元素掺杂对Au-MoS2界面肖特基势垒的影响和Se掺杂对Au-BP界面肖特基势垒的影响。研究结果表明,F和Cl原子的掺杂将会降低Au-MoS2体系的肖特基势垒高度,相比之下,Br和I原子的掺杂却增大了Au-MoS2体系的肖特基势垒高度,通过差分电荷密度和布居分布的分析,阐明了肖特基势垒高度的被调制是因为电荷转移形成的界面偶极矩的作用导致;Se原子掺杂能够有效降低Au-BP界面肖特基势垒高度,这与实验上得到的结果是一致的,通过分析掺杂前后界面间的电荷密度,解释了Au-BP界面肖特基势垒高度降低的原因。
[Abstract]:Two-dimensional materials show great potential in the field of electrical and photoelectron with its unusual physical properties. For devices, such as field effect transistors, semiconductor two-dimensional materials require metal contact electrodes, and semiconductor metal contacts tend to form a Schottky barrier at the interface. How to form low resistance contact is a challenge, This is very important for high open current, large optical response and high frequency operation. Based on the first principle of density functional theory, this paper studies the intrinsic properties of two dimensional materials, the influence of doping on the electronic structure of two dimensional materials, the contact of the metal - 2-D material to the Schottky barrier and the doping to the metal - two-dimensional material interface Schott The specific contents of the base barrier include: 1. the most stable structure of graphite, MoS2, WS2 and black phosphorus was studied by the method of first principle, and the lattice constant of the corresponding primary energy and the lattice constant of the body material was obtained, based on the lattice constant of the optimized bulk material graphite, MoS2, WS2 and black phosphorus, and the corresponding single layer structure was established. The stable single-layer two-dimensional materials are obtained by atomic relaxation. The energy band and state density of graphene, single layer MoS2, single layer WS2 and single layer BP are calculated by the Exchange Association of LDA and GGA respectively. The results show that graphene is 0 band gap semi metal, single layer MoS2, single layer WS2 and single layer BP are direct band gap semiconductor.3.. On the basis of good MoS2 lattice constant, 3 x 3 x 1 single layer MoS2 supercell is established, and the defect formation energy of S vacancy and Mo vacancy is studied. It is found that the defect formation of S vacancy can be smaller than that of Mo vacancy, which indicates that the defects of S vacancy form are easier to form, which is in agreement with the conclusion that the S vacancy is easily produced by the pure MoS2 surface. Ef (F) Ef (I) Ef (Cl) Ef (Br) is found by the substitution of different halogen atoms for the doping of S atoms, which indicates that the F atom in a single layer MoS2 is the most easily doped, and the Br atom is difficult to add a single layer to the single layer to calculate the band and state density of the stable structure after the substitution of the halogen atom. The lattice constant of the impurity energy level.4. is introduced in the band gap, and the metal - 2-D material interface is established in the form of the lattice constant of the metal matching two-dimensional material, including: (1) Mg-graphene, Cu-graphene, Al-graphene, Au-graphene, Pt-graphene. The metal pair is studied by the first principle method based on the density functional theory. The modulation effect of Fermi energy level of graphene shows that the Fermi level of Mg, Cu and Al metals belongs to n regulation, while Au and Pt control the Fermi level of graphene belongs to p type regulation, and the results are in agreement with the literature. (2) Mg-MoS2, Al-MoS2, Cu-MoS2, Au-MoS2, Ti-MoS2 MoS2 contact with single layer MoS2 is n type contact, and the Schottky barrier formed by Mg, Al, and single layer MoS2 is relatively low, which is closer to Ohm contact, while Au, Ti, Ni, Pt, Pd and single-layer MoS2 form the high height of Schottky barrier, which is a typical Schottky contact. The Schottky barrier formed by Cu, Al and monolayer WS2 is lower and closer to Ohm contact, while Au, Ni, Ti, Pt, Pd and single-layer WS2 contact are high, and the Schottky barrier is the typical Schottky contact; (4) Al-BP, Au-BP. The results show that the potential barrier formed by the contact of Al and black phosphorus is lower than that formed by contact with black phosphorus. Compared to Au, Al may be a better metal electrode.5.. The effect of the halogen element doping on the Schottky barrier of the Au-MoS2 interface and the influence of Se doping on the Schottky barrier at the Au-BP interface are investigated by the first principle method. The results show that the doping of F and Cl atoms will reduce the Schottky barrier height of the Au-MoS2 body, by contrast, Br and I. The doping of the atom increases the Schottky barrier height of the Au-MoS2 system. Through the analysis of the difference charge density and distribution, it is stated that the modulation of the Schottky barrier height is caused by the effect of the interface dipole moment formed by the charge transfer; the doping of the Se atom can effectively reduce the Schottky barrier height of the Au-BP interface, which is in the experiment. The results obtained are consistent. By analyzing the charge density between the interfaces before and after doping, the reason for the reduction of Schottky barrier height at Au-BP interface is explained.
【学位授予单位】：中国科学院大学(中国科学院上海技术物理研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304

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