With the ever shrinking devices sizes following Moore’s law, heat dissipation becomes a bottle-neck issue for semiconductor industry. Discovering new materials with ultrahigh thermal conductivity can lead to efficient thermal management and has been intensively investigated by recent theories. In particular, a new semiconductor, boron arsenide (BAs) has been predicted to have ultrahigh thermal conductivity by ab initio calculations. However, experimental development has been scarce and challenged by crystal quality. Here, we report our recent experimental development in synthesizing single-crystal BAs with minimum defects and measured a record-high thermal conductivity of 1300 W/mK beyond all bulk semiconductors and metals. To better understand the fundamental origin of such high thermal conductivity, we performed advanced phonon spectroscopy. Our measurements reveal that, unlike the commonly accepted rule for most materials that the three-phonon process is the only dominant scattering mechanism, high-order anharmonicity through the four-phonon process is significant in BAs because of its unique band structure. In addition, we probed the phonon spectra through ballistic transport and show that phonons with long mean free paths are the major contributors to the BAs and BP thermal conductivity. Our study established BAs as a new benchmark thermal management material and underscores the promise of discovering advanced thermal materials through experimental-theory synergy.
1. Joon Sang Kang, Man Li, Huan Wu, Huuduy Nguyen, and Yongjie Hu, “Experimental observation of high thermal conductivity in boron arsenide,” Science 361, 575-578 (2018).
2.Joon Sang Kang, Huan Wu, and Yongjie Hu, “Thermal Properties and Phonon Spectral Characterization of Synthetic Boron Phosphide for High Thermal Conductivity Applications,” Nano Letters 17, 7507 (2017).
3. Joon Sang Kang, Ming Ke, and Yongjie Hu, "Ionic Intercalation in Two-Dimensional van der Waals Materials: In Situ Characterization and Electrochemical Control of the Anisotropic Thermal Conductivity of Black Phosphorus," Nano Letters 17, 1431–1438 (2017).
4. Zhaoyang Lin*, Courtney Hollar*, Joon Sang Kang* (co-first author) et al., "A Solution Processable High Performance Thermoelectric Copper Selenide Thin Film," Advanced Materials 29, 1606662 (2017).
5. Man Li, Joon Sang Kang, and Yongjie Hu, "Anisotropic thermal conductivity measurement using a new Asymmetric-Beam Time-Domain Thermoreflectance (AB-TDTR) method," Review of Scientific Instruments 89, 084901 (2018).