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arXiv 1302.0694cond-mat.mes-hall
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包含声子散射的石墨烯纳米场效应晶体管紧束缚输运模拟的模式空间方法

Mode space approach for tight-binding transport simulations in graphene nanoribbon field-effect transistors including phonon scattering

Roberto Grassi, Antonio Gnudi, Ilaria Imperiale, Elena Gnani, Susanna Reggiani, Giorgio Baccarani

摘要:

在本文中,我们提出了一个模式空间方法的原子非平衡格林函数模拟扶手椅型石墨烯纳米管场效应晶体管,包括电子-声子散射。参考传统和隧道FET结构,我们表明,在一个平滑的静电势的理想情况下,模式可以在不同组中去耦,而不会有任何损失的准确性。因此,由于电子-声子相互作用的子带间散射被适当地考虑,而整体模拟时间相对于真实空间大大提高,对于1.5 nm宽的设备具有40的加速因子。该因子随着器件宽度的平方而增加。我们还讨论了两种常用的散射自能近似的精度:忽略非对角项的模式空间表达式和忽略厄米部分的延迟自能。虽然后者在大多数偏置条件下是可接受的近似值,但当器件处于关断状态时,前者有些不准确,并且光学声子散射在通过带到带隧穿确定电流时至关重要。最后,我们表明,在无序势的存在下,耦合模式空间的方法是必要的,但结果仍然是准确的实空间的解决方案相比。

英文摘要:

In this paper, we present a mode space method for atomistic non-equilibrium Green's function simulations of armchair graphene nanoribbon FETs that includes electron-phonon scattering. With reference to both conventional and tunnel FET structures, we show that, in the ideal case of a smooth electrostatic potential, the modes can be decoupled in different groups without any loss of accuracy. Thus, inter-subband scattering due to electron-phonon interactions is properly accounted for, while the overall simulation time considerably improves with respect to real-space, with a speed-up factor of 40 for a 1.5-nm-wide device. Such factor increases with the square of the device width. We also discuss the accuracy of two commonly used approximations of the scattering self-energies: the neglect of the off-diagonal entries in the mode-space expressions and the neglect of the Hermitian part of the retarded self-energy. While the latter is an acceptable approximation in most bias conditions, the former is somewhat inaccurate when the device is in the off-state and optical phonon scattering is essential in determining the current via band-to-band tunneling. Finally, we show that, in the presence of a disordered potential, a coupled mode space approach is necessary, but the results are still accurate compared to the real-space solution.

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