石墨炔与锡烯层状体系的形变势和电声耦合及载流子传输理论研究

Theoretical Studies on the Deformation Potential, Electron-Phonon Coupling, and Carrier Transports of Layered Systems

我们对sp+sp^2杂化的碳同素异形体—石墨炔,以及锡烯等层状体系的电子结构、形变势、电声耦合和电荷输运性质进行了回顾。有些二维石墨炔具有类似石墨烯的狄拉克锥,同时石墨炔电子结构可通过将其沿不同方向裁剪成不同宽度一维纳米带来调节。采用玻尔兹曼输运方程和形变势近似,结合第一性原理计算,我们预测石墨炔电荷载流子室温迁移率可达10~4–10~5 cm2?V^(-1)?s^(-1),尤其6,6,12-石墨炔,因有两个狄拉克锥及比石墨烯弱的电声耦合,其室温迁移率甚至能高于石墨烯。因此具有独特电子结构和高迁移率的石墨炔能成为继石墨烯之后未来的纳米电子器件材料。此外我们着重分析了形变势方法的适用性:密度泛函微扰理论和瓦尼尔插值技术能精确计算任意波矢和模式的声子对载流子散射,该方法在石墨烯和石墨炔上的运用表明二维平面碳材料中对载流子输运起主导作用的是长波长纵声学声子散射,因而形变势方法是适用的;但通过对锡烯等二维非平面buckling结构的材料声子散射和迁移率的计算,发现此类不具备σh对称性的材料有较强的面外声子散射和横声学声子谷间散射,使得常用的形变势失效。

The electronic structures,deformation potential,electron-phonon couplings(EPCs),and intrinsic charge transport of layered systems-the sp+sp2 hybridized carbon allotropes,graphynes(GYs)and graphdiynes(GDYs),as well as sp2+sp3 hybridized structure with buckling,such as stanine-have been investigated theoretically.Computational studies showed that,similar to graphene,some GYs can possess Dirac cones(such asα-,β-,and 6,6,12-GYs),and that the electronic properties of GYs and GDYs can be tuned by cutting into nanoribbons with different widths and edge morphologies.Focusing on the features of Dirac cones,band structure engineering can provide a clue for tuning electronic transport in 2D carbon-based materials.Based on the Boltzmann transport equation and the deformation potential approximation(DPA),the charge carrier mobilities in GYs and GDYs were predicted to be as high as 104–105 cm2?V?1?s?1 at room temperature.Interestingly,due to lower EPC strength and longer relaxation time,the charge carrier mobility in 6,6,12-GY with double Dirac cones structure was found to be even larger than that of graphene at room temperature.The unique electronic properties and high mobilities of GYs and GDYs make them highly promising candidates for applications in next generation nanoelectronics.Additionally,through the full evaluation of the EPC by density functional perturbation theory(DFPT)and Wannier interpolation,the EPCs with different phonon branches and wave-vectors as well as charge carrier mobilities for graphene,GYs and stanene have been discussed.This showed that the longitudinal acoustic(LA)phonon scattering in the long wavelength limit is the main scattering mechanism for GYs and graphene,and thus the DPA is applicable.Due to stronger LA phonon scattering,the electron mobilities(~104 cm2?V?1?s?1)ofα-GYs andγ-GYs were predicted to be one order of magnitude smaller than that of graphene at room temperature by full evaluation of the EPC.However,the DPA would fail if there was buckling in the honeycomb structure and the planar symmetry was broken(absence ofσh),such as in stanene,where the inter-valley scatterings from the out-of-plane acoustic(ZA)and transverse acoustic(TA)phonons dominate the carrier transport process and limit the electron mobilities to be(2–3)×103 cm2?V?1?s?1 at room temperature.In addition to our calculations,others have also found that the main scattering mechanisms in layered systems with buckling,such as silicene and germanene,are ZA and TA phonons.Thus,these results give us new insights into the role of EPCs and the limitation of the DPA for carrier transport in layered systems.They also indicate that the carrier mobilities of systems withoutσh-symmetry can be improved by suppressing the out-of-plane vibrations,for example by clamping by a substrate.