Parametrization of a silicon nanowire effective mass model from sp~3d~5s~* orbital basis calculations

摘要

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 sp~3d~5s~* atomic orbital basis tight-binding calculations. The nanowires used in this study are grown in (100) and (110) 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 (110) 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.