Temperature measurements of metal-free GaN using a thermoreflectance-based approach depending on excitation wavelength

Abstract This study provides a precise and reproducible methodology of measuring the surface temperature of GaN devices without metal deposition, based on thermoreflectance (TR) properties. Two TR techniques are proposed, tailored to the reflectance properties of GaN devices. The first method measures the surface temperature by monitoring changes in reflectance using light with an energy above the bandgap, while the second method monitors changes in the fringe pattern of the reflectance spectrum using light with a sub-bandgap energy of GaN. Both methods can measure equally accurate surface temperatures across a wide range of temperature by improving the magnitude and nonlinearity of the temperature-dependent reflectance through appropriate selections of incident light wavelengths. This research is expected to be applicable for non-contact and non-destructive measurement of local temperatures in high-power electronic and optoelectronic devices based on GaN across a wide temperature range.