Achieving Ultrahigh Thermal Conductivity and Carrier Mobility in Boron Arsenide Single Crystals

Thermal management becomes a critical technological challenge in the modern microelectronics world, including high power density electronics like microprocessors, high-power radio frequency (RF) devices and optoelectronic devices. When modern electronic devices are made with shrinking the size, the excess heat generation rises that reduces the device’s performance, efficiency and life span. Materials with high thermal conductivity are crucial to improve the performance and reliability of such devices. In theory, heat is transferred via conduction, convection and radiation, of which direct conduction is the easiest and fastest way. Thus, researchers are looking for materials with higher thermal conductivity, but developing a passive cooling solution that is both cost-effective and reliable has been very challenging because of the difficulties in synthesis, high cost and the requirement of extreme laboratory conditions. Boron arsenide (BAs) with zinc blende structure has been predicted to have an ultrahigh thermal conductivity close to 2000 W m-1 K-1 at room temperature by first-principle calculations, which close to diamond. However, experimental synthesis for large-scale proved to be extremely challenging, due to spontaneous nucleation and slow growth rates. Here we report an enhanced CVT growth of BAs single crystals with more controlled nucleation and optimized growth parameters for the purpose of achieving very high thermal conductivity. We have obtained high-quality BAs single crystals with the largest size of 7 mm and highest thermal conductivity of 1240 W m-1 K-1 grown using GaAs wafers, which is much higher than most of the industry-leading heat sink materials. Furthermore, we performed electrical and optical characterizations on high-quality BAs and obtained bulk carrier mobility of 650 cm2 V-1 s-1 by transport method and local mobility of ~1500 cm2 V-1 s-1 by optical method. From optical measurements, we obtained an indirect bandgap of 2.0 eV for BAs, which proven that BAs is the only known wide bandgap semiconductor to have ultrahigh thermal conductivity. Such enhancements make BAs suits for more and more characterizations and leading to new research of potential future semiconductor applications. Further improvements on BAs seem to be very promising towards extensive fundamental studies and industry applications.