Parametrization of a silicon nanowire effective mass model from sp3d5s* orbital basis calculations

Abstract

We parameterize a silicon nanowire effective mass model to facilitate device simulation, where the mass depends on the wire dimension. Parametrization is performed for n-channel silicon nanowire transistors from sp3d5s* atomic orbital basis tight-binding calculations. The nanowires used in this study are grown in ⟨1 0 0⟩ and ⟨1 1 0⟩ directions. With the parameterized nanowire effective masses, we then calculate the current and compare against the full band I–V. The full band I–V is calculated for ⟨1 1 0⟩ wires of cross sections 0.82 nm × 0.82 nm and 1.2 nm× 1.2 nm due to computational resource limitation. The full-band and effective-mass I–V characteristics of 1.2 nm × 1.2 nm wire show very good agreement. However, a relatively larger mismatch is observed for the 0.82 nm × 0.82 nm wire, especially at the lower gate biases. This is because the current has both the thermal and tunneling components, and the nanowire effective-mass model overestimates the tunneling current. This overestimation is relatively larger for thinner wires. The thermal component of current is the same in both the nanowire effective-mass and full-band models. The performance metrics, namely the intrinsic switching delay and the unity current gain frequency are evaluated from the full-band calculations. The device has a near ideal subthreshold slope, a fraction of picosecond switching delay and a tera Hertz unity current gain frequency.