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

R. Grassi, A. Gnudi, I. Imperiale, E. Gnani, S. Reggiani, G. Baccarani

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9 Scopus citations

Abstract

In this paper, we present a mode space method for atomistic non-equilibrium Greens function simulations of armchair graphene nanoribbon field effect transistors (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.

Original languageEnglish (US)
Article number144506
JournalJournal of Applied Physics
Volume113
Issue number14
DOIs
StatePublished - Apr 14 2013
Externally publishedYes

Bibliographical note

Funding Information:
R.G. would like to thank Dr. E. Baravelli of University of Bologna for fruitful discussions on the mode-space approach. This work has been supported by the EU project GRADE 317839. The authors acknowledge the CINECA Award No. HP10CPFJ69, 2011 for the availability of high performance computing resources and support.

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