Hu Research Laboratory at UCLA
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Boron Arsenide: Crystal Synthesis, Ultrahigh Thermal Conductivity, and Semiconductor Cooling

Our cubic boron arsenide research connects materials discovery with semiconductor cooling and fundamental phonon transport—from high-quality crystal synthesis to thermal interfaces, GaN device integration, and room-temperature phonon focusing.

Boron arsenide for semiconductor thermal management
Research image from the UCLA H-Lab website.

Background: why cubic boron arsenide matters

Cubic boron arsenide (BAs) is a III–V semiconductor in which boron and arsenic form a zinc-blende crystal structure. Its exceptional ability to conduct heat makes it an important material for studying phonon transport and developing semiconductor cooling technologies. Effective cooling depends on both intrinsic material properties and the interfaces through which heat reaches a cooling substrate or heat spreader.

First-principles theory by Lucas Lindsay, David Broido, and Thomas Reinecke calculated high thermal conductivity in BAs, motivating efforts to understand its unusual phonon spectrum and scattering mechanisms. Experimental confirmation required overcoming difficult crystal-growth and defect-control challenges: defects and impurities scatter phonons and can obscure the intrinsic heat-conduction capability. High-quality crystal synthesis therefore became central to connecting the theoretical prediction with measured material behavior.

Materials discovery and ultrahigh thermal conductivity

Our group pioneered the chemical synthesis of high-quality boron arsenide (BAs) single crystals and experimentally demonstrated a room-temperature thermal conductivity of approximately 1300 W/(m·K), establishing BAs as an ultrahigh-thermal-conductivity semiconductor [Science 361, 575 (2018) · Download PDF]. Overcoming crystal-growth and defect-control challenges was essential to revealing the material’s exceptional heat-conduction capability and confirming theoretical predictions of ultrahigh thermal conductivity.

By combining materials synthesis, precision thermal measurements, spectroscopy, and first-principles theory, this work established BAs as a benchmark semiconductor for understanding phonon transport and developing advanced thermal management technologies.

We also developed a database of basic physical properties of cubic BAs [Applied Physics Letters 115, 122103 (2019) · Download PDF], providing a foundation for materials characterization, device design, and semiconductor integration.

Device applications and semiconductor integration

Our 2021 studies translated this materials breakthrough into device cooling. Flexible, self-assembled BAs thermal interface materials combine efficient heat conduction with softness and mechanical compliance [Nature Communications 12, 1284 (2021) · Download PDF]. BAs cooling substrates integrated with operating gallium nitride devices demonstrate the importance of heterogeneous integration and interface engineering for reducing hotspot temperatures [Nature Electronics 4, 416 (2021) · Download PDF].

These advances provide a foundation for semiconductor cooling, power electronics, and advanced electronic packaging, with opportunities for thermal management of AI hardware.

Fundamental transport physics and room-temperature phonon focusing

We investigate the microscopic origins of ultrahigh thermal conductivity in BAs, including long phonon mean free paths and higher-order four-phonon scattering. Our study of high-pressure thermal transport [Nature 612, 459 (2022) · Download PDF] provided experimental evidence for substantial four-phonon contributions, establishing BAs as an exception to the conventional picture of room-temperature heat conduction dominated by three-phonon scattering.

Our subsequent demonstration of room-temperature phonon focusing [Nature Physics 22, 1416 (2026) · Download PDF] revealed symmetry-guided, wave-like heat propagation and focused, ray-like temperature distributions. Experiments and first-principles calculations connect crystal orientation and nonequilibrium phonons with long propagation lengths to directional heat flow beyond conventional diffusion.

These findings motivate future quantum thermal engineering, including investigation of phonon interactions with electronic and other excitations, with potential relevance to energy systems, electronics, and quantum technologies.

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