Measurement of Self-Heating Temperature in AlGaN/GaN HEMTs by Using Cerium Oxide Micro-Raman Thermometers

A new experimental technique to characterize the self-heating temperature of biased AlGaN/GaN high-electron-mobility transistors (HEMTs) is presented in this article. This method involves using micro-Raman thermography and CeO
₂
microparticles deposited on the GaN semiconductor and the metal ohmic and gate contacts of the AlGaN/GaN HEMTs. Thus, it allows estimating the self-heating temperature of these biased devices not only from the changes with the component temperature in the phonon frequencies but also from the linewidth of Raman lines related to the CeO
₂
microparticles. In these conditions, the characterization of the metal surfaces by Raman thermography becomes possible by using these CeO
₂
Raman microthermometers although the metal material cannot be characterized directly by Raman spectroscopy. Moreover, transparency of the CeO
₂
microparticles also permits to measure the temperature of volumetric GaN/AlGaN layers. Henceforth, the Raman spectroscopy is the only technique that offers the possibility of simultaneously measuring the self-heating temperature in the well-defined volume in the GaN semiconductor layers, of the semiconductor surface, the metal ohmic and gate contacts, and the substrate of the biased components.