Keeping it Cool

Abstract

We have calculated the thermal conductivities ( ) of cubic III-V boron compounds using a predictive first principles approach. Boron arsenide is found to have a remarkable room temperature over 2000 W m À1 K À1 ; this is comparable to those in diamond and graphite, which are the highest bulk values known. We trace this behavior in boron arsenide to an interplay of certain basic vibrational properties that lie outside of the conventional guidelines in searching for high materials, and to relatively weak phononisotope scattering. We also find that cubic boron nitride and boron antimonide will have high with isotopic purification. This work provides new insight into the nature of thermal transport at a quantitative level and predicts a new ultrahigh material of potential interest for passive cooling applications. DOI: 10.1103/PhysRevLett.111.025901 PACS numbers: 66.70.Àf, 63.20.kg, 71.15.Àm As microelectronic devices become smaller, faster, and more powerful, thermal management is becoming a critical challenge in, e.g., microprocessors, LEDs, and high power RF devices. As a result, the ability to identify and understand materials with high thermal conductivities ( ) is becoming increasingly important [1]. Carbon based materials, including diamond and graphite, have long been recognized as having the highest of any bulk material with room temperature (RT) values around 2000 W m À1 K À1 [2,3]. Other high materials, such as copper, are not even close, having four to five times smaller values [4]. However, diamond is scarce and its synthetic fabrication suffers from slow growth rates, high cost, and low quality [5]. Thus it is of current interest to identify new materials with ultrahigh thermal conductivities.Commonly accepted criteria [4] to guide the search for high nonmetallic crystals include (i) simple crystal structure, (ii) low average atomic mass, M av , (iii) strong interatomic bonding, and (iv) low anharmonicity. Items (ii) and (iii) imply a large Debye temperature, D , and give the frequently used rule of thumb that decreases with increasing M av and with decreasing D . However, little progress has been made over the years in identifying new high materials.Until recently fully microscopic, parameter-free computational materials techniques for electronic properties have been more advanced than are those for thermal transport. In the last few years quantitative ab initio techniques have been developed for thermal transport [6-12], and we have made contributions to this development [6,7,12]. These techniques open the way to a fuller understanding of the key physical features in thermal transport and to the ability to predict accurately the of new materials. Here, we present quantitative, first principles calculations of for the class of boron based cubic III-V compounds, boron nitride (BN), boron phosphide (BP), boron arsenide (BAs), and boron antimonide (BSb), referred to collectively as BX compounds. We find that BAs has an exceptionally high RT above 2000 W m À1 K À1 , which is comparable to that of the ...

Experimental observation of high thermal conductivity in boron arsenide

“…Here, we synthesized high-quality single-crystal BAs and measured an ultrahigh thermal conductivity of 1300 W/m•K in our BAs crystals. This value exceeds that of most HTC materials and is consistent with the ab initio prediction (8,(16)(17)(18). We characterized our samples with scanning electron microscopy, Raman spectroscopy, powder x-ray diffraction (P-XRD), single-crystal x-ray diffraction (S-XRD), and high-resolution transmission electron microscopy (HRTEM).…”

“…Recent ab initio theoretical work indicates that the conventional criteria for HTC materials are incomplete and points to new ones stemming from fundamental vibrational properties that can lead to HTC (8,(16)(17)(18). These new criteria applied to binary compounds are (i) a large mass ratio of constituent atoms; (ii) bunching together of the acoustic phonon branches; and (iii) an isotopically pure heavy atom.…”

“…This predicted HTC exceeds that of most state-of-the-art HTC materials and more than triples that of the current industrial HTC standard, i.e., silicon carbide. BAs possesses an advantageous combination of properties that incorporates both conventional (light boron mass and stiff, almost pure, covalent bonding) and new criteria [large arsenic-to-boron mass ratio, bunching together of its acoustic phonon branches, and isotopically pure As (heavy) atom] (8,(16)(17)(18).…”

“…Experimental efforts to synthesize and characterize BAs have been scarce (17). Although the growth of cubic BAs was reported in the 1950s, its detailed structural characterization and properties were not reported (23)(24)(25)(26)(27)(28).…”

“…Criteria (i) and (ii) contribute to unusually weak phonon-phonon scattering (20) and a large intrinsic thermal conductivity, whereas criteria (i) and (iii) cause relatively weak scattering of phonons by isotopes (21,22). The ab initio theory identified the III-V zinc-blende compound, defect-free boron arsenide (BAs), as having an exceptionally high thermal conductivity of more than 1000 W/m•K (8,(16)(17)(18). This predicted HTC exceeds that of most state-of-the-art HTC materials and more than triples that of the current industrial HTC standard, i.e., silicon carbide.…”