High-thermal-conductivity polycrystalline diamond grown on GaN via a cyclic-methane-modulation-assisted strategy

The self-heating effect severely limits the performance and reliability of GaN high-electron-mobility transistors (HEMTs). Direct deposition of thin-film polycrystalline diamond (PCD) on GaN is regarded as a promising strategy as it allows the heat spreader to be placed as close as possible to the hotspots. However, rapid grain coalescence during the initial growth stage usually leads to the formation of high-density graphitic carbon phases, which significantly degrades the thermal conductivity (k) of the as-grown diamond films. Here, we report a cyclic-methane-modulation-assisted (CMMA) two-step growth strategy with periodically cycled methane concentration that balances the growth rate and grain quality while suppressing the incorporation of graphite. This approach achieves a remarkably high k of 632 ± 76 W/m K for 2.4-μm-thick PCD on GaN, accompanied by a low thermal boundary resistance of 8.5 ± 0.5 m2 K/GW even with a 5 nm-thick SiNx interlayer. Finite-element simulation predicts a 70 °C reduction in peak temperature for the HEMTs integrated with CMMA-grown diamond, which highlights its substantial potential for effective thermal dissipation in high-power electronic applications.