Substrate-Dependence of Monolayer MoS${}_2$ Thermal Conductivity and Thermal Boundary Conductance

Abstract

The thermal properties of two-dimensional (2D) materials, like MoS${}_2$, are known to be affected by interactions with their environment, but this has primarily been studied only with SiO${}_2$ substrates. Here, we compare the thermal conductivity (TC) and thermal boundary conductance (TBC) of monolayer MoS${}_2$ on amorphous (a-) and crystalline (c-) SiO${}_2$, AlN, Al${}_2$O${}_3$, and $\text{h}$-BN monolayers using molecular dynamics. The room temperature TC of MoS${}_2$ is ~38 Wm${}^{-1}$K${}^{-1}$ on amorphous substrates and up to ~68 Wm${}^{-1}$K${}^{-1}$ on crystalline substrates, with most of the difference due to substrate interactions with long-wavelength MoS${}_2$ phonons (< 2 THz). An $\text{h}$-BN monolayer used as a buffer between MoS${}_2$ and the substrate causes the MoS${}_2$ TC to increase by up to 50%. Length-dependent calculations reveal TC size effects below ~2 $\mu$m and show that the MoS${}_2$ TC is size- but not substrate-limited below ~100 nm. We also find that the TBC of MoS${}_2$ with c-Al${}_2$O${}_3$ is over twice that with c-AlN despite a similar MoS${}_2$ TC on both, indicating that the TC and TBC could be tuned independently. Finally, we compare the thermal resistance of MoS${}_2$ transistors on all substrates to show that MoS${}_2$ TBC is the most important parameter for heat removal for long-channel (> 150 nm) devices, while TBC and TC are equally important for short channels. This work provides important insights for electro-thermal applications of 2D materials on various substrates.

arXiv comment16 Pages, 6 Figures, Supplementary Information

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