二硫化钨/石墨烯异质结的界面相互作用及其肖特基调控的理论研究
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摘要
采用第一性原理方法研究了二硫化钨/石墨烯异质结的界面结合作用以及电子性质,结果表明在二硫化钨/石墨烯异质结中,其界面相互作用是微弱的范德瓦耳斯力.能带计算结果显示异质结中二硫化钨和石墨烯各自的电子性质得到了保留,同时,由于石墨烯的结合作用,二硫化钨呈现出n型半导体.通过改变界面的层间距可以调控二硫化钼/石墨烯异质结的肖特基势垒类型,层间距增大,肖特基将从p型转变为n型接触.三维电荷密度差分图表明,负电荷聚集在二硫化钨附近,正电荷聚集在石墨烯附近,从而在界面处形成内建电场.肖特基势垒变化与界面电荷流动密切相关,平面平均电荷密度差分图显示,随着层间距逐渐增大,界面电荷转移越来越弱,且空间电荷聚集区位置向石墨烯层方向靠近,导致费米能级向上平移,证实了肖特基势垒随着层间距的增加由p型接触向n型转变.本文的研究结果将为二维范德瓦耳斯场效应管的设计与制作提供指导.
Two-dimensional(2D) materials exhibit massive potential in research and development in the scientific world due to their unique electrical, optical, thermal and mechanical properties. Graphene is an earliest found two-dimensional material, which has many excellent properties, such as high carrier mobility and large surface area. However, single layer graphene has a zero band gap, which limits its response in electronic devices. Unlike graphene, the transition metal sulfides(TMDs) have various band structures and chemical compositions, which greatly compensate for the defect of zero gap in graphene. The WS_2 is one of the 2D TMDs exhibiting a series of unique properties, such as strong spin-orbit coupling, band splitting and high nonlinear susceptibility, which make it possess many applications in semiconducting optoelectronics and micro/nano-electronics. The 2D semiconductors along with semimetallic graphene are seen as basic building blocks for a new generation of nanoelectronic devices. In this way, the artificially designed TMD heterostructure is a promising option for ultrathin photodetectors. There are few reports on the physical mechanism of carrier mobility and charge distribution at the interface of WS_2/graphene heterostructure, by varying the interfacial distance of WS_2/graphene heterostructure to investigate the effect on the electronic properties. Here in this work, the corresponding effects of interface cohesive interaction and electronic properties of WS_2/graphene heterostructure are studied by first-principles method. The calculation results indicate that the lattice mismatch between monolayer WS_2 and graphene is low, the equilibrium layer distance d of about 3.42 ? for the WS_2/graphene heterostructure and a weak van der Waals interaction forms in interface. Further, by analyzing the energy band structures and the three-dimensional charge density difference of WS_2/graphene, we can identify that at the interface of the WS_2 layer there appears an obvious electron accumulation: positive charges are accumulated near to the graphene layer, showing that WS_2 is an n-type semiconductor due to the combination with graphene. Furthermore, the total density of states and corresponding partial density of states of WS_2/graphene heterostructure are investigated, and the results show that the valence band is composed of hybrid orbitals of W 5 d and C 2 p, whereas the conduction band is comprised of W 5 d and S 3 p orbitals, the orbital hybridization between W 5 d and S 3 p will cause photogenerated electrons to transfer easily from the internal W atoms to the external S atoms, thereby forming a build-in internal electric field from graphene to WS_2. Finally, by varying the interfacial distance for analyzing the Schottky barrier transition, as the interfacial distance is changed greatly from 2.4 ? to 4.2 ?, the shape of the band changes slightly, however, the Fermi level descends relatively gradually, which can achieve the transition from a p-type Schottky contact to an n-type Schottky contact in the WS_2/graphene. The plane-averaged charge density difference proves that the interfacial charge transfer and the Fermi level shift are the reasons for determining the Schottky barrier transition in the WS_2/graphene heterostructure. Our studies may prove to be instrumental in the future design and fabrication of van der Waals based field effect transistors.
Two-dimensional(2D) materials exhibit massive potential in research and development in the scientific world due to their unique electrical, optical, thermal and mechanical properties. Graphene is an earliest found two-dimensional material, which has many excellent properties, such as high carrier mobility and large surface area. However, single layer graphene has a zero band gap, which limits its response in electronic devices. Unlike graphene, the transition metal sulfides(TMDs) have various band structures and chemical compositions, which greatly compensate for the defect of zero gap in graphene. The WS_2 is one of the 2D TMDs exhibiting a series of unique properties, such as strong spin-orbit coupling, band splitting and high nonlinear susceptibility, which make it possess many applications in semiconducting optoelectronics and micro/nano-electronics. The 2D semiconductors along with semimetallic graphene are seen as basic building blocks for a new generation of nanoelectronic devices. In this way, the artificially designed TMD heterostructure is a promising option for ultrathin photodetectors. There are few reports on the physical mechanism of carrier mobility and charge distribution at the interface of WS_2/graphene heterostructure, by varying the interfacial distance of WS_2/graphene heterostructure to investigate the effect on the electronic properties. Here in this work, the corresponding effects of interface cohesive interaction and electronic properties of WS_2/graphene heterostructure are studied by first-principles method. The calculation results indicate that the lattice mismatch between monolayer WS_2 and graphene is low, the equilibrium layer distance d of about 3.42 ? for the WS_2/graphene heterostructure and a weak van der Waals interaction forms in interface. Further, by analyzing the energy band structures and the three-dimensional charge density difference of WS_2/graphene, we can identify that at the interface of the WS_2 layer there appears an obvious electron accumulation: positive charges are accumulated near to the graphene layer, showing that WS_2 is an n-type semiconductor due to the combination with graphene. Furthermore, the total density of states and corresponding partial density of states of WS_2/graphene heterostructure are investigated, and the results show that the valence band is composed of hybrid orbitals of W 5 d and C 2 p, whereas the conduction band is comprised of W 5 d and S 3 p orbitals, the orbital hybridization between W 5 d and S 3 p will cause photogenerated electrons to transfer easily from the internal W atoms to the external S atoms, thereby forming a build-in internal electric field from graphene to WS_2. Finally, by varying the interfacial distance for analyzing the Schottky barrier transition, as the interfacial distance is changed greatly from 2.4 ? to 4.2 ?, the shape of the band changes slightly, however, the Fermi level descends relatively gradually, which can achieve the transition from a p-type Schottky contact to an n-type Schottky contact in the WS_2/graphene. The plane-averaged charge density difference proves that the interfacial charge transfer and the Fermi level shift are the reasons for determining the Schottky barrier transition in the WS_2/graphene heterostructure. Our studies may prove to be instrumental in the future design and fabrication of van der Waals based field effect transistors.
引文
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[2] Wen B, Cao M S, Lu M M, Cao W Q, Shi H L, Liu J, Wang X X, Jin H B, Fang X Y, Wang W Z, Yuan J 2014 Adv.Mater. 26 3484
[3] Cao M S, Wang X X, Cao W Q, Fang X Y, Wen B, Yuan J2018 Small 14 1800987
[4] Cao M S, Song W L, Hou Z L, Wen B, Yuan J 2010 Carbon48 788
[5] Liu Z F, Liu Q, Huang Y, Ma Y F, Yin S G, Zhang X Y, Sun W, Chen Y S 2008 Adv. Mater. 20 3924
[6] Castro N A H, Guinea F, Peres N M R, Novoselov K S, Geim A K 2009 Rev. Mod. Phys. 81 109
[7] Ferrari A C, Meyer J C, Scardaci V, Casiraghi C, Lazzeri M,Mauri F, Piscanec S, Jiang D, Novoselov K S, Roth S, Geim A K 2006 Phys. Rev. Lett. 97 187401
[8] Zhao H, Guo Q S, Xia F N, Wang H 2015 Nanophotonics 4128
[9] Yang L Y, Sinitsyn N A, Chen W B, Yuan J T, Zhang J, Lou J, Crooker S A 2015 Nat. Phys. 11 830
[10] Zeng H L, Liu G B, Dai J F, Yan Y J, Zhu B R, He R C, Xie L S, Xu J, Chen X H, Yao W, Cui X D 2013 Sci. Rep. 3 1608
[11] Britnell L, Ribeiro R M, Eckmann A, Jalil R, Belle B D,Mishchenko A Y J, Gorbachev R V, Georgiou T, Morozov S V, Grigorenko A N, Geim A K, Casiraghi C, Neto A H C,Novoselov K S 2013 Science 340 1311
[12] Georgiou T, Yang H F, Jalil R, Chapman J, Novoselov K S,Mishchenko A 2014 Dalton Trans. 43 10388
[13] Chen K T, Chang S T H 2017 Vacuum 140 172
[14] Cong C X, Shang J Z, Wang Y L, Yu T 2018 Adv. Opt.Mater. 6 1700767
[15] Iqbal M W, Iqbal M Z, Khan M F 2016 RSC Adv. 6 24675
[16] Yue Y, Chen J, Zhang Y, Ding S, Zhao F, Wang Y, Feng W2018 ACS Appl. Mater. Interfaces DOI:10.1021/acsami.8b05885
[17] Hong X,Kim J,Shi S F,Zhang Y, Jin C, Sun Y, Tongay S,Wu J, Zhang Y, Wang F 2014 Nat. Nanotechnol. 9 682
[18] Ma Y D, Dai Y, Guo M, Niu C W, Huang B B 2011Nanoscale 3 3883
[19] Li X D, Yu S, Wu S Q, Wen Y H, Zhou S, Zhu Z Z 2013 J.Phys. Chem. C 117 15347
[20] Dean C R, Young A F, Meric I, Lee C, Wang L, Sorgenfrei S,Watanabe K, Taniguchi T,Kim P, Shepard K L, Hone J2010 Nat. Nanotechnol. 5 722
[21] Lin X, Xu Y, Hakro A A, Hasan T, Hao R, Zhang B L, Chen H S 2013 J. Mater. Chem. C1 1618
[22] Xue J M,Sanchez-Yamagishi J, Bulmash D, Jacquod P,Deshpande A, Watanabe K, Taniguchi T, Jarillo Herrero P,Leroy B J 2011 Nat. Mater. 10 282
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[24] Cai Y, Chu C P, Wei C M, Chou M Y 2013 Matter Mater.Phys. 88 245408
[25] Zhang F, Li W, Ma Y Q, Tang Y N, Dai X Q 2017 RSC Adv.7 29350
[26] Tan H J, Xu W S, Sheng Y W, Lau C S, Fan Y, Chen Q,Wang X C, Zhou Y Q, Warner J H 2017 Adv. Mater. 291702917
[27] Wei Y, Ma X G, Zhu L, He H, Huang C Y 2017 Acta Phys.Sin. 66 087101(in Chinese)[危阳,马新国,祝林,贺华,黄楚云2017物理学报66 087101]
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[29] Liu B, Wu L J, Zhao Y Q, Wang L Z, Cai M Q 2016 RSC Adv. 6 60271
[30] Jiang J W 2015 Front. Phys. 10 287
[31] Segall M D, Lindan P J D, Probert M J, Pickard C J, Hasnip P J, Clark S J, Payne M C 2002 J. Phys.:Condens. Matter.14 2717
[32] Vanderbilt D 1990 Phys. Rev. B 41 7892
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[34] Monkhorst H J, Pack J D 1976 Phys. Rev. B 13 5188
[35] Ma X G, Hu J S, He H, Dong S J, Huang C Y, Chen X B2018 ACS Appl. Nano Mater. 1 5507
[36] Bjorkman T, Gulans A, Krasheninnikov A V, Nieminen R M2012 Phys. Rev. Lett. 108 235502
[37] Hu J S, Ji G P, Ma X G, He H, Huang C Y 2018 Appl. Surf.Sci. 440 35
[38] Ding Y, Wang Y L, Ni J, Shi L, Shi S Q, Tang W H 2011Physica B 406 2254
[39] Du A J, Sanvito S, Li Z, Wang D W, Jiao Y, Liao T, Sun Q,Ng Y H, Zhu Z H, Amal R, Smith S C 2012 J. Am. Chem.Soc. 134 4393
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[41] Li X E, Basile L, Huang B 2015 ACS Nano 9 8078
[42] Wang Q H, Kalantar-Zadeh K, Kis A 2012 Nature Nanotechnol. 7 699
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[44] Fang X Y, Yu X X, Zheng H M, Jin B, Wang L, Cao M S2015 Phys.Lett.A 379 2245