Effects of Chirality and Diameter on Electron Transport Properties in Individual Semiconducting Carbon Nanotubes
- PDF / 136,565 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 31 Downloads / 237 Views
1017-DD08-49
Effects of Chirality and Diameter on Electron Transport Properties in Individual Semiconducting Carbon Nanotubes M. Zahed Kauser and P. Paul Ruden Electrical and Computer Engineering, University of Minnesota, 200 Union St. SE., Room 4-174, Minneapolis, MN, 55455
ABSTRACT We report on the effects of chirality and diameter on the electron transport properties in individual semiconducting, single wall carbon nanotubes. The Boltzmann transport equation is solved indirectly by the Ensemble Monte Carlo method and directly by Rodeís iterative technique. Results show considerable effects of chirality and group on band structure and transport properties of tubes with small diameters. However the effects of chirality and group become negligible for tubes with large diameters. Diameter affects these properties more strongly than either chirality or group. INTRODUCTION Carbon nanotubes (CNTs) may be the most promising nano-materials studied to date. They 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. 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]. Chiral (n,m) CNTs are less studied, primarily because of their complicated electron and phonon dispersions associated with low symmetry. Recently, we proposed a technique that simplifies the problem and we reported interesting effects of chirality and group (defined by n-m mod 3 equal to ±1) on the transport properties of semiconducting CNTs with similar diameters [8,9]. A comprehensive study of electron transport properties as a function of both chirality and diameter is still lacking in the literature. In this paper, we report on the effects of chirality and diameter on the electronic structure and transport properties of (n,m) CNTs of arbitrary chirality. Ensemble Monte Carlo (EMC) simulations and Rodeís iterative technique are used to calculate the high and low-field transport properties, respectively. 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 steadystate phenomena are explored for various electric fields. To get a reasonably complete understanding, CNTs with diameters from 0.78 nm to 3.88 nm are simulated.
THEORY Electronic band structures The electronic band structures for a (n,m) CNTs are calculated by zone-folding the π and π* bands of graphene [10]. The graphene bands are obtained by tight binding (TB) method taking into account the nearest neighbor hopping matrix elements, γ i (i=1,2,3). The 1-D dispersion relations of the lowest
Data Loading...
