Heat Diffusion Governing Universal Trend in Saturation Current and Power in AlGaN/GaN High Electron Mobility Transistors in Pulsed Operation

We report the universal trend in pulsed-DC and RF operations of GaN-based high electron mobility transistors through reduced peak junction temperature governed by heat diffusion. The saturation drain current (IDS,SAT) is known to increase with reducing duty cycle D and pulse period P. The improved IDS,SAT is due to enhanced heat diffusion during OFF-time for smaller D. Contrary to the reported linear trend, this work discovers a power-law dependency between high IDS,SAT versus D for all measured conditions. The estimated junction temperature also shows a universal power-law trend with IDS,SAT. The previously reported linear trend, valid over a limited D and/ or temperature, is an approximation to the most general trend observed here. The effect of surface/buffer trapping/de-trapping is not significant to mask the universal trend. Fourier's law fundamentally governs the slope in the log-log scale through heat diffusion, which is the root cause of the discovered universal behavior. The universal trend provides further insights into the operations of these transistors. The GaN HEMTs under pulsed-DC and RF operation provide significantly higher gain up to large input power, lower gain compression, and higher power-added efficiency (PAE) following the universal law. Peak power handling capacity increases with decreasing D following the power-law relation. Peak output power, average power output, and PAE show a strict linear trend in the log-log scale with D, establishing its fundamental dependency on the junction temperature. Considering the root cause of the fundamental nature, it is likely that the same universal relation persists for all transistors under pulsed operation.