Self-Heating in a GaN-Based Heterojunction Field-Effect Transistor Investigated by Ultraviolet and Visible Micro-Raman Spectroscopy

Direct measurements are reported of self-heating in an AlGaN/GaN transistor using ultraviolet and visible micro-Raman. Device stack is comprised of silicon substrate, AlN nucleation, AlGaN transition, GaN buffer, and AlGaN barrier layers. Phonon shifts are used to estimate temperature rise. Ultraviolet measurements probe the current- carrying GaN near the interface. Visible micro- Raman measurements provide an average temperature rise through GaN, AlN, and substrate near its interface with AlN. Under identical drive conditions, temperature rises from UV micro-Raman are approximately twice those from visible measurements. Correlating the data with a thermal simulation provides an estimated thermal boundary resistance 1×10^.8 K.m²/W.