Thermal Transport in Single-Layer MoS2 and Black Phosphorus Transistors

Ballistic thermal conductance in single-layer MoS2 and black phosphorus (BP) is calculated based on the phonon dispersion. In single-layer MoS2, the ballistic thermal conductance is almost isotropic of a value of 10.7x10(8) W/m(2)K; while in single-layer BP, the in-plane ballistic thermal conductance is anisotropic with a value of 12.8 x 10(8) W/m(2)K in the zigzag direction and 7.1 x 10(8) W/m(2)K in the armchair direction. Thermal transport behaviors at both steady state and transient state in double-gated MOSFET-like transistors with single-layer MoS2 and BP used as the channel material are studied. The conventional Fourier's law with contact temperatures as the boundary conditions and modified boundary conditions that can capture quasi-ballistic phonon transport effects are used. The simulation results show that Fourier's law with contact temperatures as the boundary conditions underestimate the peak temperature rise by 64% in single-layer MoS2 transistors and 56% in single-layer BP transistors when the channel length is comparable to the phonon mean free path. And the strong anisotropic thermal properties of single-layer BP lead to higher temperature rise in the armchair direction than that in the zigzag direction.