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锗烷因其合适的带隙、较高的电子迁移速率、较好的环境稳定性、较小的电噪声和超薄的几何结构, 有望取代现有硅基或锗基材料成为下一代半导体器件的理想载体. 基于密度泛函理论和非平衡格林函数的第一性原理方法, 研究了不同构型和浓度的氢空位簇对锗烷电子结构及锗烷中四硫富瓦烯(tetrathiafulvalene, TTF)分子掺杂性能的影响. 计算结果表明, 不同构型氢空位簇的引入可诱导GermananeDehydrogenated-xH (GD–xH) 体系产生不同性质的磁性, 且磁矩大小亦与Lieb定理的预测结果相符, 并能在GD-xH (x = 1, 4, 6) 体系自旋向下的能带结构中实现由缺陷态引起的类p型半导体掺杂效应, 其电子激发所需的能量则会随着体系脱氢浓度的升高而不断降低. 吸附TTF分子后, G/TTF和GD-xH/TTF (x = 1, 2, 6)体系表现出分子掺杂效应, 且GD-xH/TTF (x = 1, 6)体系因分子轨道与缺陷态的杂化作用, 可在自旋向上与自旋向下的能带结构中形成不同的掺杂类型. 进一步的量子输运计算还表明, Armchair和Zigzag类型的锗烷基器件表现为明显的各向同性, 且TTF分子吸附所导致的载流子掺杂可大幅提高其I-V特性.Germanane is expected to substitute for existing silicon-based or germanium-based material. Germanane is regarded as an ideal candidate for next-generation semiconductor material due to its suitable band gap, high electron mobility, better environmental stability, small electrical noise and ultrathin geometry. In this work, the effects of different configuration and concentration of hydrogen vacancy cluster on the electronic properties of germanane and its molecular doping are systematically investigated through the first-principles method based on density functional theory and none-quilibrium Green’s function. The results show that the hydrogen vacancy clusters with different configurations can induce magnetism with different characteristics in GermananeDehydrogenated-xH (GD-xH) system, and the magnetic moments are consistent with the predictions of Lieb’s theorem. Moreover, the p-type-liked doping effects caused by defective state under GD-xH (x = 1, 4, 6) systems can be realized in their spin-down band structures. The corresponding energy values for exciting electron would gradually decrease with the increase of the concentration of hydrogen vacancy clusters under different configurations. After adsorbing tetrathiafulvalene (TTF) molecules, G/TTF and GD-xH/TTF (x = 1, 2, 6) systems exhibit molecular doping characteristics induced by the TTF molecules. More importantly, for GD-xH/TTF (x = 1, 6) system, the different molecular doping types can be introduced in spin-up and spin-down band structures due to the hybridization composed of molecular orbitals and defective states under spin polarization. Further calculations of their transport properties indicate that germanane-based device with Armchair and Zigzag configurations both exhibit intensive isotropy, and the performance of I-V characteristics can be dramatically enhanced owing to the carrier doping by TTF adsorption.
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Keywords:
- germanane /
- defect /
- molecular adsorption /
- electronic properties
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图 1 锗烷中典型的4种氢空位簇构型俯视图(蓝色和绿色小球分别代表Ge和H原子) (a) GD-1H; (b) GD-2H; (c) GD-4H; (d) GD-6H
Fig. 1. Top view of four typical configurations for different hydrogen vacancy clusters in germanane: (a) GD-1H; (b) GD-2H; (c) GD-4H; (d) GD-6H. Blue and green spherules represent Ge and H atoms, respectively.
图 2 (a)—(e) 锗烷和不同氢空位簇锗烷 GD-xH (x = 1, 2, 4, 6)体系对应的能带结构; (f) Eg, Ep和体系磁矩随脱氢浓度的变化
Fig. 2. (a)–(e) Corresponding band structures of germanane and different hydrogen vacancy clusters GD-xH (x = 1, 2, 4, 6) systems; (f) Eg, Ep and magnetic moment as a function of dehydrogenation concentration.
图 3 G/TTF和GD\text{-}xH/TTF (x = 1, 2, 4, 6)体系最佳吸附构型的俯视图和侧视图 (a) G/TTF, H2-site; (b) GD-1H/TTF, V2-side; (c) GD-2H/TTF, B2-side; (d) GD-4H/TTF, H2-side; (e) GD-6H/TTF, V2-side. 蓝色、绿色、红色和棕色小球分别代表Ge, H, S和C原子
Fig. 3. Top and side views of optimal adsorption configuration of G/TTF and GD–xH/TTF (x = 1, 2, 4, 6) systems : (a) G/TTF, H2-site; (b) GD-1H/TTF, V2-side; (c) GD-2H/TTF, B2-side; (d) GD-4H/TTF, H2-side; (e) GD-6H/TTF, V2-side. Blue, green, red and brown spheres represent Ge, H, S, and C atoms, respectively.
图 4 (a) G/TTF和 (b)—(e) GD-xH/TTF (x = 1, 2, 4, 6)体系对应能带结构, 其中绿色和粉色平带分别代表由TTF分子贡献和脱氢处的Ge原子贡献, 橙色平带代表由TTF分子和脱氢处Ge原子共同贡献; (f) Eg, En, Ep和体系净磁矩随脱氢浓度的变化
Fig. 4. Corresponding band structures of (a) G/TTF and (b)–(e) GD-xH/TTF (x = 1, 2, 4, 6) systems, where green and pink flat bands represent contribution of TTF molecule and Ge atoms at dehydrogenation, respectively, orange flat bands represent the joint contribution of TTF molecule and Ge atom at dehydrogenation; (f) Eg, En, Ep and magnetic moment as a function of dehydrogenation concentration.
图 5 (a) G/TTF和(b)—(e) GD-xH/TTF (x = 1, 2, 4, 6)体系的HOMO和LUMO, 其中等值面设为 0.004 e/Å3
Fig. 5. HOMO and LUMO in the (a) G/TTF and (b)–(e) GD-xH/TTF (x = 1, 2, 4, 6) systems. Isosurface level is set to 0.004 e/Å3.
图 6 (a)—(e) G/TTF和GD-xH/TTF (x = 1, 2, 4, 6)体系的差分电荷密度俯视和侧视图, 其中青色和黄色分别代表失电荷和得电荷; 等值面设为0.0002 e/Å3 (a)和 0.001 e/Å3 (b)—(e)
Fig. 6. (a)–(e) Top and side views of differential charge density for G/TTF and GD–xH/TTF (x = 1, 2, 4, 6) systems. Cyan and yellow color represents deficiency and accumulation of electron, respectively. Isosurface is set to 0.0002 e/Å3 and 0.001 e/Å3 in panel (a) and (b)–(e), respectively.
图 7 基于 Armchair (a)和Zigzag(b)构型的锗烷基纳米器件模型
Fig. 7. Germanane-based nanodevice model with Armchair (a) and Zigzag (b) type configurations.
图 8 Armchair (a)和Zigzag(b)类型的锗烷纳米器件模型的电子透射谱和态密度图, 其中蓝色实线表示透射谱曲线, 绿色虚线表示态密度
Fig. 8. Electron transmission spectra and DOS along Armchair (a) and Zigzag (b) directions in germanane-based nanodevice model. Blue implementation represents the transmission spectral curve, and the green dashed line represents the DOS.
图 9 本征锗烷(a)、G/TTF(b)和GD-xH/TTF (x = 1, 2) (c), (d)基器件的I-V特性曲线
Fig. 9. I-V characteristic curves for devices based on intrinsic germanane (a), G/TTF (b) and GD-xH/TTF (x = 1, 2) (c), (d).
表 1 本征锗烷和脱氢锗烷的磁矩、Ge—H键长、Ge—Ge键长以及Ge原子的平均褶皱高度
Table 1. Magnetic moment, Ge—H bond length, Ge—Ge bond length and the average height of the Ge atoms in different configurations of dehydrogenated germanane.
参数 Germanane GD-1H GD-2H GD-4H GD-6H $ \mu /{\mu }_{{\rm{B}}} $ 0 1.000 0 2.000 0 ${d}_{ {\rm{G} }{\rm{e} }\text{—}{\rm{H} } }/$Å 1.561 1.561—1.568 1.562—1.567 1.562—1.567 1.564—1.570 ${d}_{ {\rm{G} }{\rm{e} }\text{—}{\rm{G} }{\rm{e} } }$/Å 2.467 2.465—2.487 2.345—2.493 2.430—2.492 2.415—2.492 Δ/Å 0.725 0.726 0.733 0.734 0.735 
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表 2 G/TTF和GD-xH/TTF (x = 1, 2, 4, 6)体系最佳吸附构型所对应的吸附能, 净磁矩, 结构参数和电荷转移量
Table 2. Adsorption energy, magnetic moment, structural parameters and charge transfer of optimal adsorption configuration of G/TTF and GD-xH/TTF (x = 1, 2, 4, 6) systems.
参数 G/TTF GD-1H/TTF GD-2H/TTF GD-4H/TTF GD-6H/TTF $ {E}_{{\rm{a}}{\rm{d}}} $/eV 0.583 0.889 0.766 0.895 1.230 $ \mu $/$ {\mu }_{{\rm{B}}} $ 0 1.000 0 2.000 0 d/Å 4.592 4.294 4.307 3.737 3.527 ${d}_{ {\rm{G} }{\rm{e} }\text{—}{\rm{G} }{\rm{e} } }$/Å 2.468—2.470 2.467—2.523 2.384—2.501 2.469—2.506 2.423—2.517 ${d}_{ {\rm{G} }{\rm{e} }\text{—}{\rm{H} } }$/Å 1.560—1.568 1.563—1.571 1.563—1.571 1.563—1.577 1.563—1.570 Δ/Å 0.735 0.738 0.734 0.739 0.736 Q/e 0.029 0.392 0.195 0.230 0.200
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[1] Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, Firsov A A 2004 Science 306 666
Google Scholar
[2] Zhang Y, Tan Y W, Stormer H L, Kim P 2005 Nature 438 201
Google Scholar
[3] Novoselov K S, Geim A K, Morozov S V, Jiang D, Katsnelson M I, Grigorieva I V, Dubonos S V, Firsov A A 2005 Nature 438 197
Google Scholar
[4] Du X, Skachko I, Barker A, Andrei E Y 2008 Nat. Nanotechnol. 3 491
Google Scholar
[5] Bianco E, Butler S, Jiang S, Restrepo O D, Windl W, Goldberger J E 2013 ACS Nano 7 4414
Google Scholar
[6] Sahoo N G, Esteves R J, Punetha V D, Pestov D, Arachchige I U, McLeskey J T 2016 Appl. Phys. Lett. 109 023507
Google Scholar
[7] Madhushankar B N, Kaverzin A, Giousis T, Potsi G, Gournis D, Rudolf P, Blake G R, van der Wal C H, van Wees B J 2017 2D Mater. 4 021009
Google Scholar
[8] Hu L, Zhao J, Yang J 2014 J. Phys. Condens. Matter. 26 335302
Google Scholar
[9] Li Y, Chen Z 2014 J. Phys. Chem. C 118 1148
Google Scholar
[10] Ma Y, Dai Y, Lu Y B, Huang B 2014 J. Mater. Chem. C 2 1125
Google Scholar
[11] Zhou Y, Liu K, Xiao H, Xiang X, Nie J, Li S, Huang H, Zu X 2015 J. Mater. Chem. C 3 3128
Google Scholar
[12] Zhao J, Zeng H 2016 RSC Adv. 6 28298
Google Scholar
[13] Chandiramouli R 2017 J. Mol. Liq. 242 571
Google Scholar
[14] Kannan V, Ganesan V, Vijayakumar V 2022 Comput. Theor. Chem. 1214 113799
Google Scholar
[15] Vajda S, Pellin M J, Greeley J P, Marshall C L, Curtiss L A, Ballentine G A, Elam J W, Catillon-Mucherie S, Redfern P C, Mehmood F, Zapol P 2009 Nat. Mater. 8 213
Google Scholar
[16] Zhou S, Zhao J 2016 J. Phys. Chem. C 120 21691
Google Scholar
[17] Wang X, Liu G, Liu R F, Luo W W, Wu M S, Sun B Z, Lei X L, Ouyang C Y, Xu B 2018 Nanotechnology 29 465202
Google Scholar
[18] Cui Z, Luo Y, Yu J, Xu Y 2021 Physica E 134 114873
Google Scholar
[19] Yan H, Ma W 2022 Adv. Funct. Mater. 32 2111351
Google Scholar
[20] Qin Z, Gao C, Wong W W H, Riede M K, Wang T, Dong H, Zhen Y, Hu W 2020 J. Mater. Chem. C 8 14996
Google Scholar
[21] Ye J P, Liu G, Han Y, Luo W W, Sun B Z, Lei X L, Xu B, Ouyang C Y, Zhang H L 2019 Phys. Chem. Chem. Phys. 21 20287
Google Scholar
[22] Blöchl P E 1994 Phys. Rev. B 50 17953
Google Scholar
[23] Kresse G, Furthmüller J 1996 Phys. Rev. B 54 11169
Google Scholar
[24] Monkhorst H J, Pack J D 1976 Phys. Rev. B 13 5188
Google Scholar
[25] Grimme S, Antony J, Ehrlich S, Krieg H 2010 J. Chem. Phys. 132 154104
Google Scholar
[26] Henkelman G, Arnaldsson A, Jónsson H 2006 Comput. Mater. Sci. 36 354
Google Scholar
[27] Taylor J, Guo H, Wang J 2001 Phys. Rev. B 63 245407
Google Scholar
[28] Brandbyge M, Mozos J L, Ordejón P, Taylor J, Stokbro K 2002 Phys. Rev. B 65 165401
Google Scholar
[29] Yang W, Cao Y, Han J, Lin X, Wang X, Wei G, Lv C, Bournel A, Zhao W 2021 Nanoscale 13 862
Google Scholar
[30] Ali M, Pi X, Liu Y, Yang D 2017 AIP Adv. 7 045308
Google Scholar
[31] Kuklin A V, Begunovich L V, Gao L, Zhang H, Ågren H 2021 Phys. Rev. B 104 134109
Google Scholar
[32] 黄炳铨, 周铁戈, 吴道雄, 张召富, 李百奎 2019 68 246301
Google Scholar
Huang B Q, Zhou T G, Wu D X, Zhang Z F, Li B K 2019 Acta Phys. Sin. 68 246301
Google Scholar
[33] Hongzhiwei Technology 2021 Device Studio (Version 2021B) (Shanghai)
[34] 武红, 李峰 2016 65 096801
Google Scholar
Wu H, Li F 2016 Acta Phys. Sin. 65 096801
Google Scholar
[35] Liu L, Ji Y, Liu L 2019 Bull. Mater. Sci. 42 157
Google Scholar
[36] Lieb E H 1989 Phys. Rev. Lett. 62 1201
Google Scholar
[37] Neto A H C, Guinea F, Peres N M R, Novoselov K S, Geim A K 2009 Rev. Mod. Phys. 81 109
Google Scholar
[38] Kiriya D, Tosun M, Zhao P, Kang J S, Javey A 2014 J. Am. Chem. Soc. 136 7853
Google Scholar
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