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Model for Far From Equilibrium Transport in CNT/GNR FETs

By Paolo Michetti

University of Pisa

Simulation of CNT/GNR FETs including inelastic scattering via virtual probes approach and accounting for the presence of possible Schottky barrier contacts.

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Version 1.0 - published on 09 Jul 2010

doi:10.4231/D3RN3072R cite this

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Abstract

This tool solve the output and transfer characteristics for a field-effect-transistor based on carbon nanotubes or graphene nanoribbons. The solution is obtained with a semi-analytical model, which treats the device electrostatics within the long-channel approximation, but include the effect of possible tunneling Schottky barriers at source and drain, as they frequetly affects the behavior of carbon-based devices. Tunneling is treated within WKB approximation, multiple reflection/tunneling processes are properly taken into account, assuming a complete phase-randomization along the device.

Transport in real nano-devices is surely out-of equilibrium, but still it is not ballistic, however much of the semi-analytical model, but also much of the numerical simulation, are restricted to the ballistic limit. Our model is able to reproduce the continuous transition from ballistic to drain-diffusion transport regimes, and indeed any degree of inelastic scattering can be simulated. Dissipative processes are implemented within the virtual probes approach, in which a real FET is viewed as a suitable chain of N elementary ballistic FETs, separated by fully-thermalizing virtual probes, spaced by the “free mean path”. Inelastic scattering is restricted to the virtual reservoirs, while transport is ballistic in the elementary channels. N=1 corresponds to a ballistic regime, while large N to drift-diffusion transport. Note that we have developed an analytical approach for the solution of a N-elementary ballistic series of FET, which results to be accurate. We use our analytical approach in order to reduce computational costs, and, moreover, enables us to treat any real N, given by the ratio of the channel length and the free mean path.

We provide a number of physical quantities for characterizing the behavior of the device, such as the current/voltage output and transfer characteristics, the conductance and transconductance, the self-consistent charge and channel potential. A preliminary analysis of the device performance it is also carried out, with the evaluation of the cut-off frequency and the delay time of the transistor.

Publications

Physics-based compact model of nanoscale MOSFETs - Part I: Transition from drift-diffusion to ballistic transport, G. Mugnaini and G. Iannaccone, IEEE Trans. El. Dev. 52, 1795 (2005). Physics-based compact model of nanoscale MOSFETs - Part II: Effects of degeneracy on transport, G. Mugnaini and G. Iannaccone, IEEE Trans. El. Dev. 52, 1802 (2005). Analytical Model of Nanowire FETs in a Partially Ballistic or Dissipative Transport Regime, P. Michetti, G. Mugnaini and G. Iannaccone, IEEE Trans. El. Dev. 56, 1402 (2009). Analytical model of 1D Carbon-based Schottky-Barrier Transistors, P. Michetti and G. Iannaccone, arXiv:0909.3736.

Cite this work

Researchers should cite this work as follows:

  • Analytical model of 1D Carbon-based Schottky-Barrier Transistors, P. Michetti and G. Iannaccone, arXiv:0909.3736.
  • Paolo Michetti (2009), "Model for Far From Equilibrium Transport in CNT/GNR FETs," http://nanohub.org/resources/ffettool. (DOI: 10.4231/D3RN3072R).

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