Effects of impurities on the thermal and electrical transport properties of cubic boron arsenide
Résumé
Cubic boron arsenide (BAs) is a promising compound semiconductor for thermal management applications due to its high thermal conductivity, exceeding 1000 W m$^{-1}$ K$^{-1}$ at room temperature in high-quality samples. However, the as-grown BAs crystals usually exhibit large variations in thermal and electronic transport properties. The origin of these large variations has thus far been inconclusive. Here, we investigate the effects of impurities on the thermal and electrical properties of BAs. Time-of-flight secondary ion mass spectrometry and electron probe microanalysis measurements reveal the presence of several impurities in BAs, including Si, C, O, H, Te, Na, and I. Some of these impurities, especially Si, C, and H, could serve as shallow acceptors, leading to the p-type conducting behavior commonly measured in BAs. The thermal conductivity and hole mobility are reduced more in the samples with higher impurity concentrations due to the enhanced impurity scattering of phonons and holes, respectively. First-principles calculations are used to determine the thermal conductivity reduction induced by different impurities. The calculated results confirm the experimental trends. The substitution of O for As leads to a large bond distortion resulting from the breaking of the $T_d$ symmetry, which yields unusually strong phonon scattering with a correspondingly large reduction in thermal conductivity. Our results offer useful insights into the impurity-sensitive transport properties of BAs.