Strain-Reduction Induced Rise in Channel Temperature at Ohmic Contacts of GaN HEMTs.

Operating temperature distributions in AlGaN/GaN gateless and gated devices are characterized and analyzed using the InfraScope temperature mapping system. For the first time, a substantial rise of channel temperature at the inner ends of ohmic contacts has been observed. Synchrotron radiation-based high-resolution X-ray diffraction technique combined with drift-diffusion simulations show that strain reduction at the vicinity of ohmic contacts increases electric field at these locations, resulting in the rise of lattice temperature. The thermal coupling of a high conductive tensile region at the contacts to a low conductive channel region is an origin of the temperature rise observed in both short- and long-channel gateless devices.