A Computational Study on Electrical Contacts in Monolayer hhk-Si Field-Effect Transistors

Hybrid honeycomb-kagome silicene (hhk-Si) is a promising 2-D channel material for nanoscale field-effect transistors (FETs) due to its inherent compatibility with the silicon technology and superior intrinsic transport properties compared to other 2-D silicon. However, the electrical contact properties, critical to the performances of 2D-FETs, have not been studied for monolayer hhk-Si. Here, based on first-principles calculations and quantum-transport simulations, we systematically investigated the electrical contact interfaces of the monolayer hhk-Si with various metal electrodes (Ti, Ag, Au, Cu, and Pt). The results show that the monolayer hhk-Si on the five metal surfaces undergoes metallization, and no Schottky barrier (SB) and tunneling barrier is formed at the vertical contact interfaces. At the lateral interfaces between the hhk-Si in the source and channel regions, SBs form with severe Fermi-level pinning (FLP), exhibiting a small pinning factor of 0.13. Among them, n-type Schottky contact was formed for the Ti electrode with an electron barrier of 0.28 eV, while p-type Schottky contact exited for the Pt electrodes with a hole barrier of 0.24 eV. The simulated transfer characteristics revealed the crucial role of contact barriers on FET currents, and the extracted subthreshold swing (SS) verified the feasibility of breaking the thermal limitation by band engineering in the drain.