Self-heating in a GaN based heterostructure field effect transistor: Ultraviolet and visible Raman measurements and simulations

Abstract

We report direct self-heating measurements for AlGaN∕GaN heterostructure field effect transistor grown on SiC. Measurements are carried out using micro-Raman scattering excited by above band gap ultraviolet and below band gap visible laser light. Ultraviolet excitation probes the GaN near the AlGaN∕GaN interface region of the device where the two-dimensional electron gas carries the source-drain current. The visible excitation probes the entire ∼1μm thick GaN layer and the SiC substrate near the interface with GaN. These results thus provide a measure of the average temperature throughout the GaN and of the substrate. Results are backed by combined electrical and thermal simulations. We find that the immediate hot spot region of the device, at the edge of the gate electrode, rises by up to ∼240°C over ambient under the most aggressive drive conditions examined.