Size effects in the thermal conductivity of gallium oxide (β-Ga2O3) films grown via open-atmosphere annealing of gallium nitride

Abstract

Gallium nitride (GaN) is a widely used semiconductor for high frequency and high power devices due 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.

A Strategic Review on Gallium Oxide Based Deep‐Ultraviolet Photodetectors: Recent Progress and Future Prospects

“…For example, thinning down the material can enhance the phonon-boundary scattering resulting in better thermal transport. [245][246] However, this is an emerging field and more studies on phonon scattering in gallium oxide and at the interfaces will be of paramount importance.…”

Applications and Impacts of Nanoscale Thermal Transport in Electronics Packaging

“…1.2. In the past, thermal conductivities of doped and undoped bulk and thin film b-Ga 2 O 3 samples were measured at different temperatures using techniques such as 3x and TDTR [206][207][208]. Thermal conductivities of 300-1000 nm thick AlN thin films obtained using 3x technique are measured to be between k ¼ 5.4-17.7 W/mÁK [209].…”

Creation of Liquid Metal 3D Microstructures Using Dielectrophoresis

“…The oxide layer, which forms over the surface of Galinstan microstructures in the presence of DI water, has a thermal conductivity of 8.8 ± 3.4 W m −1 K −1 , which is lower than that of Galinstan, and therefore suppresses the heat transfer over the surface. However, the thickness of the oxide layer is in the range of 0.7–3 nm, which minimizes its thermal effect.…”