Unusual high thermal conductivity in boron arsenide bulk crystals

Abstract

Conventional theory predicts that ultrahigh lattice thermal conductivity can only occur in crystals composed of strongly bonded light elements, and that it is limited by anharmonic three-phonon processes. We report experimental evidence that departs from these long-held criteria. We measured a local room-temperature thermal conductivity exceeding 1000 watts per meter-kelvin and an average bulk value reaching 900 watts per meter-kelvin in bulk boron arsenide (BAs) crystals, where boron and arsenic are light and heavy elements, respectively. The high values are consistent with a proposal for phonon-band engineering and can only be explained by higher-order phonon processes. These findings yield insight into the physics of heat conduction in solids and show BAs to be the only known semiconductor with ultrahigh thermal conductivity.

Basic physical properties of cubic boron arsenide

“…Heat dissipation is a critical technology issue for modern electronics and photonics [1][2][3][4][5] . A key challenge and urgent need for effective thermal management is to discover new materials with ultrahigh thermal conductivity for dissipating heat from hot spots efficiently, and thereby improving device performance and reliability [6][7][8][9][10] . Options to address this challenge with conventional high thermal conductivity materials, such as diamond and cubic boron nitride, are very limited [11][12][13] ; their high cost, slow growth rate, degraded crystal quality, combined with the integration challenge with semiconductors, given chemical inertness and large mismatch in lattice and thermal expansion, make them far from optimal candidates.…”

“…Recent ab initio theory calculation has predicted new boron compounds with high thermal conductivity stemming from the fundamental vibrational spectra [15][16][17] . Although the early growth was reported in 1950s [18][19][20][21][22][23] , obtaining high-quality crystals of these materials with minimal defects has proven challenging and was only achieved very recently [6][7][8][9] . Our recent study 7 reports the successful synthesis of single-crystal BAs with non-detectable defects, along with the measurement of a record-high thermal conductivity of 1300 W/mK, a value which is beyond that of most common semiconductors and metals.…”

f-Orbital based Dirac states in a two-dimensional uranium compound

“…As opposed to common occurrence in 2D nanostructures [28], UB 4 phonon optical branches exhibit larger energy dispersion and broader distribution of phonon velocities than acoustical branches (see figure 1(c)). Due to the large difference of the atomic masses, an unusual gap between optical and acoustic modes is developed, similarly to the gap observed in bulk BAs [29][30][31] and Li 2 Te [32]. Figure 1(c) displays the phonon diagrams of the three uranium compounds with the same scale in the ordinate axis showing that this gap decreases as the mass of the atoms in the honeycombed sublattices increases.…”

Strain and electric field tuning of 2D hexagonal boron arsenide

“…Computational studies using density functional theory (DFT) reveal that boron arsenide (BAs) can form a stable 2D hexagonal structure similar to hexagonal boron nitride showing a semiconducting nature with a bandgap of approximately 1 eV [30,31]. Boron arsenide forms a cubic 3D structure with a remarkably high thermal conductivity [32,33], a property the 2D structure hexagonal boron arsenide (h-BAs) is expected to share [34,35] with application perspectives as coolant in nanodevices. In [30] they explore the effect of biaxial strain on the electronic structure and find a transition to a metallic state at a biaxial strain of 14%.…”