In recent years, significant progress in understanding the physics of carbon nanotube electronic devices and in identifying potential applications has occurred. In a nanotube, low bias transport can be nearly ballistic across distances of several hundred nanometers. Deposition of high-κ gate insulators does not degrade the carrier mobility. The conduction and valence bands are symmetric, which is advantageous for complementary applications. The bandstructure is direct, which enables optical emission. Because of these attractive features, carbon nanotubes are receiving much attention. In this work, simulation approaches are developed and applied to understand carbon nanotube device physics, and to explore device engineering issues for better transistor performance.
Carbon nanotube field-effect transistors (CNTFETs) provide a concrete context for exploring device physics and developing a simulation capability. We have developed an empirical (p z orbital) atomistic, quantum simulator for nanotube transistors. This simulator uses the non-equilibrium Green's function (NEGF) formalism to treat ballistic transport in the presence of self-consistent electrostatics. We also separately developed a coupled Monte-Carlo/quantum injection simulator to understand carrier scattering in CNTFETs.
Numerical simulations are used to understand device physics and to explore device engineering issues. In chapter 4, we did a comprehensive study of the scaling behaviors for ballistic SB CNTFETs. In chapter 5, we analyzed a short-channel, high-performance CNTFET, to understand what controls and how to further improve the transistor performance. In chapter 6, we explored the interesting role of phonon scattering in CNTFETs.
