Quantum mechanical simulation of hole transport in p-type Si nanowire schottky barrier MOSFETs

Abstract

Recently, SB-MOSFETs with metallic source/drain have attracted attention as an alternative for the conventional MOSFETs due to their improved scaling property and low parasitics. As metal oxide semiconductor devices shrink down to nanometer regime, quantum mechanical effects is coming up to play an important role in their device performance. In particular, SB-MOSFETs are operated by tunneling current through the Schottky barrier, and thus, in assessing the device performance of SB-MOSFETs, it is of fundamental importance to accurately calculate tunneling current quantum mechanically. In this work, p-type nanowire SB-MOSFETs are simulated based on the k.p method, which is one of well-known methods to describe Si valence band structure, by self-consistently solving the Poisson equation and non-equilibrium Green`s function (NEGF). In this work, we have discussed about basics of SB-MOSFETs such as operating principles in the On- and Off-state, and the ambipolar behavior. The effect of spin-orbit coupling in the valence band is calculated and we found that it is almost negligible in the final I-V characteristics. The uncoupled mode approach is briefly introduced as an analysis tool to know information. The band warping due to coupling of holes is seen in the k.p method, and mode-coupling is absent in the uncoupled mode approach. The short channel effect and high-k gate dielectric effect are finally investigated and the devices show a strong dependence on the transport direction in terms of subthreshold slope, On-state current, threshold voltage shift, and tunneling distance, due to the orientation-sensitive tunneling effective mass, the confinement energy, and the tunneling distance. It would be expected that, the high-k gate dielectric gives performance improvement and the scaling of equivalent oxide thickness is essential in the nano-scaled device to improve their performance.