An Atomistic Model for Carbon Nanotube Based Field-effect Transistors: Interband Tunneling and Device Scaling


An Atomistic Model for Carbon Nanotube Based Field-effect Transistors: Interband Tunneling and Device Scaling

Fuchs, F.; Zienert, A.; Schuster, J.; Gemming, S.

We study carbon nanotube based field-effect transistors (CNTFETs) consisting of n-doped source and drain electrodes together with an ideal wrap-around gate. This system is comparable to the one studied experimentally by Lu et al. [1] and is our model for comparing different simulation approaches. In this contribution, we present our results based on a fully atomistic quantum transport model.
Carbon nanotubes (CNTs) with diameters ranging from 0.5 nm to 1.3 nm, which corresponds to the (7,0) CNT and (16,0) CNT, respectively, are studied. We find that in case of thick CNTs, the band-to-band tunneling (BTBT) strongly increases the leakage current in the off-state. This leads to ambipolar transfer characteristics in agreement with experimental results1. Concerning very thin CNTs, the BTBT has not been studied in much detail, yet. We demonstrate that for these kind of CNTs, states within the channel are strongly localized. They do not allow carrier transport and thus suppress the BTBT, which results in ideal unipolar transfer characteristics and on/off ratios of about 107.
We furthermore present a systematic investigation of the relation between device parameters and the resulting transistor characteristics, which can guide future device scaling. Thin CNTs for example allow outstanding device properties even for short channel lengths down to 8 nm. It is crucial to maintain channel control in ultra-scaled transistors. Thus, our studies also elucidate the impact of aggressive gate scaling. Even for a very small gate electrode of only 0.4 nm length, good switching properties can be preserved.
The non-equilibrium Green’s functions formalism together with self-consistent extended Hückel theory is used for the simulations. Thanks to a parameter set previously developed in our group [2], we can describe CNTs with a density functional theory-like accuracy.
[1] Lu et al., Journal of the American Chemical Society 128 (2006)
[2] Zienert et al., Nanotechnology 25 (2014)

Keywords: carbon nanotubes; field-effect transistor; extended Hückel theory; electron transport

  • Poster
    17th International Conference on the Science and Application of Nanotubes and Low-Dimensional Materials (NT16), 28.08.-02.09.2016, Wien, Österreich

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