  Materials with high thermal conductivity are needed to conduct heat away from
hot spots in power electronics and optoelectronic devices. Cubic boron arsenide
(c-BAs) has a high thermal conductivity due to its special phonon dispersion
relation. Previous experimental studies of c-BAs report a room-temperature
thermal conductivity between 1000 and 1300 watts per meter-kelvin. We
synthesized high purity c-BAs single crystals with room-temperature thermal
conductivity of 1500 watts per meter-kelvin. We observed its thermal
conductivity to be proportional to the inverse square of temperature between
300 and 600 kelvin, a stronger dependence than predicted by state-of-the-art
theory.
