The development of gallium nitride (GaN) on a variety of substrates from SiC to diamond is under development to create high power RF technologies for advanced communications and power electronic devices. In general, GaN devices can accommodate high operational frequencies, high junction temperatures, and high voltages, allowing them to operate at higher power with increased efficiency in smaller form factors. It is expected that GaN will play a major role in rf communications and create highly efficient power converters for electronic systems operating below 600 V.  However, GaN is typically grown on non-lattice matched substrates which results in interfacial thermal resistances, dislocations, and stresses that can impede the operation and reliability of the devices.

In this talk we use a variety of experimental techniques to measure the thermal conductivity, thermal boundary resistance (TBR) and thermal performance for AlGaN/GaN layers on SiC and diamond substrates.  Metrology methods to measure these properties will be presented including Raman thermometry, thermoreflectance, and gate resistance thermometry.  An update on the status of CVD diamond layers for cooling GaN devices from the current Diamond Round Robin funded by DARPA will be discussed. Finally, the electro-thermomechanical behavior of GaN HEMTs under DC and pulsed operation will be presented where the temperature of the devices was measured using Raman Spectroscopy while the mechanical deformation was measured by Scanning Joule Expansion Microscopy.   Data will show that rapid heating and high tensile stresses near the drain side edge of the gate during pulsed operation is dependent on the bias conditions, the TBR, substrate material, and the mechanical properties of the device.  The implications of these findings on device performance and reliability will be discussed.