Quantum transport simulations of graphene nanoribbon devices using Dirac equation calibrated with tight-binding π-bond model.

Sai-Kong Chin,Gengchiau Liang,Dawei Seah,Kai-Tak Lam

doi:10.1186/1556-276x-7-114

Abstract

We present an efficient approach to study the carrier transport in graphene nanoribbon (GNR) devices using the non-equilibrium Green's function approach (NEGF) based on the Dirac equation calibrated to the tight-binding π-bond model for graphene. The approach has the advantage of the computational efficiency of the Dirac equation and still captures sufficient quantitative details of the bandstructure from the tight-binding π-bond model for graphene. We demonstrate how the exact self-energies due to the leads can be calculated in the NEGF-Dirac model. We apply our approach to GNR systems of different widths subjecting to different potential profiles to characterize their device physics. Specifically, the validity and accuracy of our approach will be demonstrated by benchmarking the density of states and transmissions characteristics with that of the more expensive transport calculations for the tight-binding π-bond model.

Highlights

Recent progress of graphene nanoribbon (GNR) fabrication has demonstrated the possibility of obtaining nanoscale width GNRs, which have been considered as one of the most promising active materials for generation electronic devices due to their unique properties such as bandgap tunability via controlling of the GNR width or subjecting GNR to external electric/magnetic fields [1,2,3,4,5]
3 Results and discussions To incorporate the material details of GNR into the TBπ model, we first fit (3) of different GNR widths with that of the tight-binding π-bond model (TB-π) model, which is widely used to calculate the bandstructures of GNR, for a flat potential (i.e., U = 0)
The E (k) calculated using (3) deviated from the that of the TB-π model. This is expected as the tightbinding Dirac equation (TBDE) model for GNR is most accurate near the Dirac points at small k [15]

Summary

Introduction

Recent progress of graphene nanoribbon (GNR) fabrication has demonstrated the possibility of obtaining nanoscale width GNRs, which have been considered as one of the most promising active materials for generation electronic devices due to their unique properties such as bandgap tunability via controlling of the GNR width or subjecting GNR to external electric/magnetic fields [1,2,3,4,5]. (See Table 1.) Figure 2 shows, as a comparison, the corresponding total computing time for calculating the all relevant surface Green’s functions (via iterative method) for the same set of GNR width in TBπ model. This time is much larger than that of the TBDE, between about 100× (at 1.1 nm width) and 455× (for 3.8 nm width) that of the analytic method of TBDE. Fs,d(E) is the Fermi function at either the source or drain, Σsb denotes sum over the subbands, Diag[...] and Tr[...] denote the diagonal and the trace of a square matrix, respectively

Results and discussions

Imaginary real

Conclusion

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