Molecular beam epitaxy of boron arsenide layers

Thermal management is the main technological challenge for next generation electronic devices. Recently, several groups successfully demonstrated boron arsenide (BAs) microcrystals with an ultrahigh thermal conductivity approaching that of diamond. The development of scalable epitaxial BAs growth techniques is urgently required to enable a transition of BAs material to real applications. We have grown boron arsenide layers on 3C-SiC/Si and sapphire substrates over a wide temperature range using molecular beam epitaxy (MBE). We have confirmed the incorporation of arsenic by a wide range of characterization techniques. The best quality of the boron arsenide layers was achieved at high growth temperatures of around 750 °C. We have demonstrated that high temperatures nucleation of the boron arsenide layer started with deposition of boron-rich monolayers on the substrate surface. For the epitaxy on sapphire during the initial growth phase, the cubic boron arsenide layers align with the hexagonal structure of the sapphire substrate and grow in the ⟨111⟩ direction for a few crystalline monolayers; however, currently, we are not able to sustain that, and the boron arsenide layer becomes amorphous. For boron arsenide layers grown at high temperatures, we have observed an increase in the thermal conductivity and cathodoluminescence optical response with a reproducible peak centered at ∼1.67 eV. The experimental results are explained by increased chemical interaction between arsenic and boron at growth temperatures above ∼600 °C. Our experimental data show that MBE growth conditions need to be further optimized first to improve stoichiometry and after that to decrease point-defect densities in boron arsenide layers to achieve an increase in the thermal conductivity.