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 nonequilibrium 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 ( ${f}_{T}$ ) and unity power gain frequency ( ${f} _{{\mathsf {max}}}$ ). To develop keen insight into practical devices, we discuss the optimization of ${f} _{T}$ and ${f} _{{\mathsf {max}}}$ by varying various device parameters such as channel length ( ${L} _{{\mathsf {ch}}}$ ), oxide thickness, device width, gate resistance, contact resistance, and parasitic capacitance. Although extrinsic ${f}_{T}$ and ${f} _{{\mathsf {max}}}$ can be significantly affected by the contact resistance and parasitic capacitance, they can remain near THz frequency range ( ${f} _{T} = \mathsf {900}$ GHz; ${f} _{{\mathsf {max}}} = \mathsf {1.2}$ THz) through proper engineering, particularly with an aggressive channel length scaling ( ${L} _{{\mathsf {ch}}} \approx \mathsf {10}$ 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 analog and radio-frequency applications.