Electron Transport in Semiconducting Chiral Carbon Nanotubes
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0922-U07-50
Electron Transport in Semiconducting Chiral Carbon Nanotubes M. Z. Kauser1, A. Verma2, and P. P. Ruden1 1 Electrical and Computer Engineering, Univeristy of Minnesota, Minneapolis, MN, 55455 2 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, 30332
ABSTRACT We report on electron transport characteristics for semiconducting, single wall, chiral carbon nanotubes. The Boltzmann transport equation is solved indirectly by the Ensemble Monte Carlo method. The basis for the transport calculations is provided by electronic structure calculations within the framework of a simple tight binding model. Scattering mechanisms considered are due to the electron-phonon interactions involving longitudinal acoustic, longitudinal optic, and radial breathing mode phonons. Results show significantly increased Umklapp scattering processes due to the reduced Brillouin zone compared to zigzag nanotubes. However, the transient and steady-state transport characteristics are similar to those of zigzag CNTs with comparable diameter. INTRODUCTION Carbon nanotubes (CNTs) have demonstrated potential to be key building blocks in the next generation of nanoscale electronic and opto-electronic devices [1,2]. However, control of the nanotube fabrication process is still a challenge. In particular, the chirality of CNTs is difficult to control. Electron transport experiments are often performed on tubes of unknown chirality, while previous theoretical work has focused on the understanding of transport in achiral, semiconducting, zigzag (n,0) CNTs, based on analytical models [3] and Monte Carlo simulations [4-7]. A recent study has shown that nanotube growth slightly favors chiral structures [8]. Thus, a complete picture of electron transport in CNTs requires an understanding of transport in chiral CNTs. However, modeling chiral (n,m) CNTs poses new challenges, primarily because of their complicated electron and phonon dispersions associated with low symmetry. In this paper, we report on electronic structure and phonon calculations for (n,m) CNTs of arbitrary chirality. Ensemble Monte Carlo (EMC) simulations for electron transport based on these calculations are performed. The principal electron scattering mechanisms are due to coupling to longitudinal acoustic (LA), longitudinal optical (LO), and radial breathing mode (RBM) phonons. Both Normal and Umklapp scattering process are considered. Transient and steady-state phenomena are explored for various electric fields. To exemplify the major differences in the transport characteristics of chiral and zigzag CNTs, the results obtained for a (11,7) CNT are compared with those for a (16,0) CNT, which has similar diameter.
THEORY Electronic band structures The electronic bandstructures for a (n,m) CNTs are calculated based on the tight binding (TB) description of the π and π* bands of graphene taking into account the nearest neighbor hopping matrix elements, γ i (i=1,2,3). By imposing cyclic boundary conditions around the periphery of the CNT, the two-dimensi
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