Assessment of High-Frequency Performance Limit of Black Phosphorus Field-Effect Transistors

Abstract

Recently gigahertz frequencies have been reported with black phosphorus (BP) field-effect transistors (FETs), yet the high-frequency performance limit has remained unexplored. Here we project the frequency limit of BP FETs based on rigorous atomistic quantum transport simulations and the small-signal circuit model. Our self-consistent non-equilibrium Green’s function (NEGF) simulation results show that semiconducting BP FETs exhibit clear saturation behaviors with the drain voltage, unlike zero-bandgap graphene devices, leading to >10 THz frequencies for both intrinsic cutoff frequency (fT) and unity power gain frequency (fmax). To develop keen insight into practical devices, we discuss the optimization of fT and fmax by varying various device parameters such as channel length (Lch), oxide thickness, device width, gate resistance, contact resistance and parasitic capacitance. Although extrinsic fT and fmax can be significantly affected by the contact resistance and parasitic capacitance, they can remain near THz frequency range (fT = 900 GHz; fmax = 1.2 THz) through proper engineering, particularly with an aggressive channel length scaling (Lch ≈ 10 nm). Our benchmark against the experimental data indicates that there still exists large room for optimization in fabrication, suggesting further advancement of high-frequency performance of state-of-the-art BP FETs for the future analogue and radio-frequency applications.