Accurate operando measurement of AlGaN/GaN HEMTs channel temperature and optimization of thermal design.

The accurate estimation of the temperature distribution of the GaN based power devices and optimization of the device structure is of great significance to possibly solve the self-heating problem, which hinders the further enhancement of the device performances. We present here the operando temperature measurement with high spatial resolution using Raman spectroscopy of AlGaN/GaN high electron mobility transistors (HEMTs) with different device structures and explore the optimization of the device thermal design accordingly. The lateral and depth temperature distributions of the single-finger HEMT were characterized. The channel temperature and self-heating effect of the device under different bias voltages were investigated. By incorporating the two-dimensional electrothermal simulation, the hotspot position can be clearly observed under the gate edge near the drain side. The channel temperature of the multi-finger HEMT was further measured and the experiment results were in agreement with the three-dimensional finite element analysis simulation results. The device structure of the multi-finger device, including the gate width, gate pitch, structure layout, substrate materials, and thickness, were then theoretically optimized to improve the heat dissipation. The peak channel temperature of the device can be reduced by 70 °C when the substrate is substituted from silicon carbide to a single crystalline diamond. These results are of great interest for the thermal management of GaN HEMT power devices and further device performance improvement.