The Electronic Structure And Transport Properties Of Chiral Carbon Nanotubes With Defects

Carbon nanotubes (CNTs) have unique electronics and optical properties which destine them to play a major role in the next generation of nanoscale electronic and optoelectronic devices. In particular, electronic transport properties of single-wall carbon nanotubes (SWCNTs) have attracted considerable experimantial and theoretical interest. Previous theoretical work has focused on the understanding of transport in achiral of zigzag (n,0), armchair (n,n). However, control of the nanotube fabrication process is still a challenge. Electronic transport experiments are often performed on tubes of unknown chirality. A recent study has show that nanotube growth slightly favors chiral CNTs. Thus, a complete picture of electron transport in CNTs requires an understanding of transport in chiral CNTs.Using the first principles density functional theory combined with noequilibrium green function technology, the paper systematically explores substitutive doping, vacancy defect in single-walled carbon nanotubes, and gets some helpful results. It is significant for the practical preparation and development of the nanotubes-based photoelectric devices.We have investigated the systems with different concentration and different distribution. It is show that the electronic structures of the chiral (6,3)carbon nanotubes with doping of nitrogen atoms are changed obviously and the transport properties are reduced. Under certain conditions the metallic single-walled carbon nanotubes convert into semiconductor. Because of large diameter, doping of nitrogen atoms make a little impact on the chiral (8,4)CNTs. The transport properties of the system are improved when the bias is small. In some cases, the doping is unfavorable to the transport properties owning to widen band gap.The simulations of the systems with different distribution show that the transport properties of the metallic nanotube are reduced obviously by co-doping of boron/nitrogen atoms. The currents-voltage curves present nonlinear variation. The transport properties change significantly with the positions of impurity atoms in the structure. When the bias is small, the transport properties of the doping nanotube which the interval is three carbons bwteen the impurity atoms are disadvantageous. The boron/nitrogen co-doping only slightly modify the rectification ratio of the nanotube. We also studied the systems with the nitrogen doping,vacancy and the compound defects composed of nitrogen and vacancy. The characteristics of the chiral (4,2) carbon nanotube can't be changed by single nitrogen atom doping,single vacancy and the compound defects composed of nitrogen doping and vacancy. but the transport properties are improved to some extent. The currents increase significantly when the bias voltage is high. The on-state voltage of the systems with nitrogen doping go down. The structure of single vacancy possesses good rectification ratio.It is one of the most promiseful methods for application to modulate the properties of nanotubes by impurity doping and defects. So that it is an important subject to investigate the properties and the device fabrication of defective nanotubes more deeply and comprehensively.