Thermal analysis of AlGaN/GaN HFETs using electro-thermal simulation and micro-Raman spectroscopy

Abstract

We report on investigation of self-heating effects in AlGaN/GaN HFETs (heterostructure field effect transistors) using numerical simulations and micro-Raman spectroscopy. In the numerical simulations, we used a temperature-dependent thermal conductivity for each constituent material. To reduce the size effect of the device, we added wide thermal diffusion regions to active device region. Both AlGaN/GaN HFETs on sapphire and SiC substrates were studied using both electro-thermal 2D (two-dimensional) simulations and also analytical 3D thermal simulations. Good agreements between the simulated and measured surface temperature distributions have been obtained, which supports the validity of simulation models. The simulated temperature distribution for HFETs on SiC substrates was found to have a much sharper peak than that on sapphire substrates. In addition, the region around the gate edge on the drain side usually showed a maximum temperature for the devices operating at drain voltages less than about 40 V, but this region shifted toward the drain side when the drain voltage was increased up to 50-80 V. These results show that micro-Raman spectroscopy can be used for high-resolution temperature measurements.