Transport and performance study of double-walled black phosphorus nanotube transistors

Abstract

Abstract Monolayer- and a few layers-black phosphorus (BP) is an emerging two-dimensional material for the post-silicon era. We study the transport mechanism and performance metrics of double-walled BP n-channel and p-channel gate-all-around nanotube (NT) transistors using a k ⋅ p Hamiltonian and a non-equilibrium Green’s function quantum simulation. We effectively use the anisotropic effective masses along the zigzag and armchair directions of BP for high performance NT field-effect transistors. The heavy mass along the zigzag direction is used for quantization to increase the carrier density, while the lighter mass along the armchair direction is used for transport to maximize the carrier injection velocity. The on-state current is governed by the thermionic transport mechanism over the top of the potential barrier, while the off-state current is predominantly governed by intra-band tunneling current. Although the lighter mass in transport direction initiates intra-band tunneling current, the device can be successfully turned on and off with a high on/off current ratio of 1.4 × 10 5 . The n-channel transistor has an on-state current of 724 µA µm−1, a subthreshold slope of 63 mV dec−1, a transconductance of 7.97 mS µm−1, a switching delay time of 3.92 ps, a cut-off frequency of 0.201 THz, and a dynamic power loss of 0.64 fJ µm−1, respectively. The corresponding performance metrics for the p-channel are 726 µA µm−1, 64 mV dec−1, 8.20 mS µm−1, 3.96 ps, 0.205 THz, and 0.65 fJ µm−1. Both the transistors are potential candidates for the International Technology Roadmap for Semiconductors 2026 low operating power devices.