This article describes a new technique for measuring temperatures in GaN HEMTs. The method is based on Raman spectroscopy and the use of cerium oxide particles that act like micro-Raman thermometers when scanned with a UV laser. As the article explains, phonon line shifts due to Raman scattering are used to estimate the temperature of GaN layers while surface temperatures are obtained through the cerium oxide particles. The results presented also verify that the particles, which are distributed over semiconductor and metal surfaces, do not modify the electric characteristics of the GaN devices.

Virtually all semiconductor materials exhibit Raman scattering which results in a frequency shift in photon energy. In this article, the authors explain how they harness this mechanism to measure the temperature of submicron structures and thereby produce high-resolution temperature maps. They review the basic theory of Raman scattering and present application examples involving high-bandgap materials as well as silicon devices.