Thermal conductivity of annealed GaN surfaces – Congrats Chet!

Chet Szwejkowski’s paper, “Size effects in the thermal conductivity of gallium oxide (beta-Ga₂O₃) films grown via open-atmosphere annealing of gallium nitride (GaN),” was recently published in Journal of Applied Physics (J. Appl. Phys. 117, 084308 (2015)). In this work, we demonstrated that the thermal conductivity of Beta-phase Ga₂O₃ that forms on the surface of GaN while annealing in open atmosphere is polycrystalline and has a thermal conductivity of 8.8 ± 3.4 W m⁻¹ K⁻¹. This relatively high thermal conductivity has major implications for annealing during the creation of GaN contacts.  Congrats Chet!!!

Abstract

Gallium nitride (GaN) is a widely used semiconductor for high frequency and high power devicesdue to of its unique electrical properties: a wide band gap, high breakdown field, and high electron mobility. However, thermal management has become a limiting factor regarding efficiency, lifetime, and advancement of GaN devices and GaN-based applications. In this work, we study the thermal conductivity of beta-phase gallium oxide (β-Ga2O3) thin films, a component of typical gate oxides used in such devices. We use time domain thermoreflectance to measure the thermal conductivity of a variety of polycrystalline β-Ga2O3 films of different thicknesses grown via open atmosphere annealing of the surfaces of GaN films on sapphire substrates. We show that the measured effective thermal conductivity of these β-Ga2O3 films can span 1.5 orders of magnitude, increasing with an increased film thickness, which is indicative of the relatively large intrinsic thermal conductivity of the β-Ga2O3 grown via this technique (8.8 ± 3.4 W m⁻¹ K⁻¹) and large mean free paths compared to typical gate dielectrics commonly used in GaN device contacts. By conducting time domain thermoreflectance (TDTR) measurements with different metal transducers (Al, Au, and Au with a Ti wetting layer), we attribute this variation in effective thermal conductivity to a combination of size effects in the β-Ga2O3 film resulting from phonon scattering at the β-Ga2O3/GaN interface and thermal transport across the β-Ga2O3/GaN interface. The measured thermal properties of open atmosphere-grown β-Ga2O3 and its interface with GaN set the stage for thermal engineering of gate contacts in high frequency GaN-based devices.

Acknowledgements

The material is based upon work partially supported by the Air Force Office of Scientific Research under AFOSR Award No. FA9550-14-1-0067 (Subaward No. 5010-UV-AFOSR-0067), the National Science Foundation (CBET-1339436) and the Commonwealth Research Commercialization Fund (CRCF) of Virginia.