Computational modeling of channel length modulation in carbon nanotube field effect transistors

We perform computational finite-element analysis and characterization of quasi-ballistic electrical transport in semiconducting carbon nanotube field effect transistors, and fit experimental electrical transport data from both suspended and substrate-bound single-walled carbon nanotube transistors. Previous studies have ignored the spatial dependence of the electrical properties and potential, preferring to focus on modeling ballistic transport. These spatial variations play an important role in several high voltage effects that are particularly important in the quasi-ballistic transport and high gate capacitance regime where most current or near-term devices operate. We show the relationship between device geometry and pinch-off, current saturation, and channel length modulation with gate capacitance in the quantum capacitance regime, and discuss computational issues such as code performance and numerical stability. Transconductance generally increases with gate capacitance, but, surprisingly, at high gate voltages it decreases with increasing gate capacitance. This model has application as a design tool in next generation carbon nanotube microelectronics technology.