Heat Dissipation in GaN Power Semiconductor Devices

In this work, a numerical study is presented of the impact of growth substrates on thermal dissipation in GaN devices. Substrates included in this study are sapphire, SiC, GaN, ZnO, and LiGaO₂. Based on a model high power HFET device with the rear side held at a fixed temperature, the maximum junction temperature in the devices were calculated using finite element analysis and compared. Both interface resistance and the effects of dislocations in the GaN layer were accounted for. Results show that state of the art devices dissipating 10 W/mm of power must be fabricated on high thermal conductivity substrates like GaN or SiC when rear side heat dissipation is utilized. In contrast, an analysis of high heat flux removal convective cooling was investigated for the application of front side heat dissipation. These results show that junction temperatures below 150°C are readily obtainable using this method and are substrate independent. The implications of the substrate independent cooling scheme are discussed.