Quantum transport in carbon nanotube transistors: Complex band structure effects

We report the subthreshold characteristics of ballistic carbon nanotube field effect transistors (CNTFETs) showing the complex band structure effect. The tunneling of carriers from source to drain through a looped complex band structure increases the subthreshold drain current, reducing the on–off current ratio. We find that nanoscale CNTFETs can perform better with a larger on–off current ratio and better subthreshold swing if the CNT has a larger band gap.