In this work, we utilize electron-phonon Monte Carlo simulations of AlGaN/GaN HEMTs to determine the energy loss rate of electrons in the channel of the transistor as a function of bias conditions. Intense energy transfer from electrons to phonons is observed near the gate edge on the drain side of such devices where the peak electric field exists. This intense energy exchange results in nanometer sized hotspots in the vicinity of the gate edge. In order to account for effects of ballistic phonon transport on temperature near the hotspots, a non-gray Discrete Ordinates Method (DOM) is used as a numerical solver for the phonon Boltzmann Transport Equation (BTE). The non-gray model accounts for dispersion effects of GaN by splitting the dispersion curve of GaN into a finite number of frequency bands. The phonons in each frequency band are assumed to have the same properties with the other phonons in the same band and the relaxation times between these bands are calculated. The results show how energy is redistributed among the available phonon bands and demonstrates which modes are most effective at transporting the thermal energy. Finally, the hotspot temperature predictions obtained by the model are compared to temperatures obtained by gray and continuum modeling approaches to show the discrepancies between different techniques.

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