Optimizing GaN-on-diamond transistor geometry for maximum output power

Recent thermography measurements have demonstrated the potential of GaN-on-diamond transistors to offer significantly reduced thermal resistance with respect to equivalent GaN-on-SiC devices. However, measurements performed to date have focused on smaller transistors which are not representative of larger power devices and do not take full advantage of the superior heat spreading provided by high thermal conductivity diamond substrates. In order to explore the possible gain in output power for AlGaN/GaN HEMTs on diamond substrates we have developed a parametric thermal model for optimizing the geometry of a GaN-on-diamond transistor cell. We use simulation input parameters that have been experimentally validated against measurements, giving a high confidence in the modelling results. We demonstrate that by optimizing the geometry of GaN-on-diamond transistors, combined which additional diamond heat spreading layers, a ∼3× increase in total output power can be gained with respect to GaN-on-SiC.