Efficient device simulations using density functional theory Hamiltonian and non-equilibrium Green's function: heterostructure mode space method and core charge approximation

An efficient device simulation methodology utilizing the density functional theory Hamiltonian and non-equilibrium Green's function is presented in this work. Its main feature is combining the heterostructure mode space method and the core charge approximation (CCA) to efficiently and robustly treat inhomogeneous devices. The heterostructure mode space method can generate an effective Hamiltonian of much smaller size for arbitrary irregular or heterostructures, enabling order-of-magnitudes faster calculations without loss of accuracy in a practical sense. The CCA provides a physical background for removing the ambiguity associated with the commonly-used effective charge approximation, enabling robust handling of defect or interface states. Four examples of Si nanowire field-effect transistors (FETs), GaSb/InAs nanowire heterojunctions, InAs nanowire tunneling FETs with defects, and NiSi2/Si/NiSi2 Schottky barrier FETs are used for demonstration.