Simultaneous measurement of temperature and thermal stress in AlGaN/GaN high electron mobility transistors using Raman scattering spectroscopy

Raman spectroscopy, utilizing both the GaN ${\text{E}}_2$ and ${\text{A}}_1\left(\text{LO}\right)$ phonon modes, has been used to simultaneously probe temperature and thermal stress in operating AlGaN/GaN high electron mobility transistors (HEMTs). Temperature and thermal stress profiles across the active region of an AlGaN/GaN HEMT were determined. The results were found to be in good agreement with thermal and thermomechanical simulations. The maximum temperature rise and thermal stress measured in the GaN layer are located close to the drain edge of the gate contact, reaching $240°\text{C}$ and −0.37 GPa, respectively, for a power dissipation of 25 W/mm (40 V).