Influence of Defects on the Thermal Conductivity Across Temperature in Ultra High Thermal Conductivity Semiconductors

High thermal conductivity materials are crucial for heat management in high-power electronics and optoelectronic devices. Diamond and cubic boron arsenide (c-BAs), which have the highest reported thermal conductivities among semiconductors, are prime candidates for these applications. We explore how defects influence the temperature-dependent thermal conductivity of these materials.

Previous studies of c-BAs report room-temperature thermal conductivities between 1,000 and 1,300 W m^-1 K^-1. We studied high-purity, isotopically enriched c-BAs single crystals exhibiting room-temperature thermal conductivities of approximately 1,500 W m^-1 K^-1. Between 300 and 600 K, the thermal conductivity follows a 1/T² dependence, stronger than predicted by state-of-the-art theory. Our findings suggest that c-BAs can achieve higher thermal conductivities than previously thought, and that three-phonon scattering rates may be lower than current theoretical predictions.

Diamond, known for its wide bandgap and remarkable room-temperature thermal conductivity (~2,200 W m^-1 K^-1), must be doped with boron (p-type) for use in power electronic devices. We investigate how boron doping affects the temperature-dependent thermal conductivity of diamond films, and bulk diamond crystals. High concentrations of boron doping (e.g., 10²⁰ cm^-3) reduce the room-temperature thermal conductivity by a factor of four and significantly alter its temperature dependence. In high-purity diamond, thermal conductivity is proportional to 1/T between 300 and 800 K. In boron-doped diamond, thermal conductivity increases by 20% between 300 and 500 K, then decreases proportionally to 1/T above 500 K. This non-monotonic behavior suggests that boron suppresses phonon transport across both high and low frequencies. The suppression of high-frequency phonons aligns with Rayleigh-like scattering from point defects, while the suppression of low-frequency phonons indicates strong hole-phonon scattering, or the formation of extended defects with an average spacing of ~800 nm.

Acknowledgement: This work was supported as part of ULTRA, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0021230.