Mixed-size diamond seeding for low-thermal-barrier growth of CVD diamond onto GaN and AlN

Smith, E.J.W. and Piracha, A.H. and Fields, D. and Pomeroy, J.W. and Mackenzie, G.R. and Abdallah, Z. and Massabuau, F. C-P. and Hinz, A.M. and Wallis, D.J. and Oliver, R.A. and Kuball, M. and May, P.W. (2020) Mixed-size diamond seeding for low-thermal-barrier growth of CVD diamond onto GaN and AlN. Carbon, 167. pp. 620-626. ISSN 0008-6223 (https://doi.org/10.1016/j.carbon.2020.05.050)

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Abstract

We report a method of growing a diamond layer via chemical vapour deposition (CVD) utilizing a mixture of microdiamond and nanodiamond seeding to give a low effective thermal boundary resistance (TBR eff) for heat-spreading applications in high-frequency, high-power electronic devices. CVD diamond was deposited onto thin layers of both GaN and AlN on Si substrates, comparing conventional nanodiamond seeding with a two-step process involving sequential seeding with microdiamond then nanodiamond. Thermal properties were determined using transient thermoreflectance (TTR), and the samples were also analysed with SEM and X-ray tomography. While diamond growth directly onto GaN proved to be unsuccessful due to poor adhesion, films grown on AlN were adherent and robust. The two-step mixed-seeding method gave TBR eff values < 6 m 2 K GW −1 that were 30 times smaller than for films grown under identical conditions but using nanodiamond seeding alone. Such remarkably low thermal barriers obtained with the mixed-seeding process offer a promising route for fabrication of high-power GaN HEMTs using diamond as a heat spreader with an AlN interlayer.

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