Abstract
The cubic boron arsenide (BAs) crystal has received extensive research attention because of its ultra-high thermal conductivity comparable to that of diamond. In this work, we performed a comprehensive study on the diffusive thermal properties of its two-dimensional (2D) counterpart, the monolayer honeycomb BAs (h-BAs), through solving the phonon Boltzmann transport equation combined with first-principles calculation. We found that unlike the pronounced contribution from out-of-plane acoustic phonons (ZA) in graphene, the high thermal conductivity (181 W m−1 K−1 at 300 K) of h-BAs is mainly contributed by in-plane phonon modes, instead of the ZA mode. This result is explained by the unique frequency-independent ‘platform’ region in the relaxation time of in-plane phonons. Moreover, we conducted a comparative study of thermal conductivity between 2D h-BAs and h-GaN, because both of them have a similar mass density. The thermal conductivity of h-BAs is one order of magnitude higher than that of h-GaN (16 W m−1 K−1), which is governed by the different phonon scattering process attributed to the opposite wavevector dependence in out-of-plane optical phonons. Our findings provide new insight into the physics of heat conduction in 2D materials, and demonstrate h-BAs to be a new thermally conductive 2D semiconductor.
Highlights
With the rapid development of miniaturization and high-power density of the electronic and optoelectronic devices, the demand for thermal management is becoming more and more important.[1,2] Diamond is a well-known highly thermally conductive bulk material
Paper the large frequency gap between acoustic and optical phonon modes. It raises up some questions, for example, what is the thermal conductivity of its 2D counterpart (h-boron arsenide (BAs))? Which phonon modes play dominant contribution to thermal conductivity? Compared with other 2D III–V honeycomb lattice, what is the unique phonon scheme in honeycomb BAs (h-BAs)? preliminary literatures reported high thermal conductivity of honeycomb BAs (hBAs),[32,33] compared with the extensive studies of thermal conductivity of graphene and honeycomb BN (h-BN), there are still many open questions
Ðħul Þnl a nl b sl where N, V, fl, n and s are the number of wave vector q points in the Brillouin zone, volume of the unit cell, the equilibrium Boltzmann distribution depending on phonon angular frequency ul, phonon group velocity and phonon relaxation time, respectively
Summary
With the rapid development of miniaturization and high-power density of the electronic and optoelectronic devices, the demand for thermal management is becoming more and more important.[1,2] Diamond is a well-known highly thermally conductive bulk material. Inspired by the ultra-high thermal conductivity of graphene,[9] the researches on thermal transport in low-dimensional system have attracted extensive attention.[10,11,12,13,14,15,16] The decreased dimension induces quantum con nement effect and alters the phonon dispersion, which further results in unique lattice thermal transport features.[17] In addition to graphene, Sahin et al.[18] has proposed 13 different 2D III–V compounds of honeycomb lattice, seven of which (AlN, GaN, InN, BN, BP, BAs and BSb) have planer structure like graphene. Phonons obey the unique phonon scattering selection rule[5,19,20] in which three-phonon processes having an odd number of ZA phonons are forbidden This mechanism can reduce phonon scattering rate by suppressing scattering channels, and enhance thermal conductivity. Paper the large frequency gap between acoustic and optical phonon modes It raises up some questions, for example, what is the thermal conductivity of its 2D counterpart (h-BAs)? The comparison of thermal transport of h-BAs with h-GaN highlights the effect of phonon spectrum on thermal transport
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