SUMMARY

One of the most significant advances in GaN devices has evolved from the AlGaN/GaN high electron mobility transistor (HEMT). Technologies that incorporate such devices span the range from next generation WiMAX stations to advanced military radar applications. As a result of the large power densities being applied to these devices intense hot spots can develop near areas of highest electric field. In order to minimize the effect that hot spot temperatures have on device reliability a detailed understanding of relevant transport mechanisms must be developed. Modeling techniques based on the Boltzmann transport equation (BTE) have revealed non-Fourier transport dynamics but have relied on unrealistic boundary conditions as well as simplified phonon physics. The simplified phonon picture with such models have not resolved the details of the energy “bottleneck” associated with the electron-optical phonon-acoustic phonon decay channel caused by the long relaxation times of optical phonons. These long relaxation times can give rise to a capacitive effect, which when neglected will result in an under prediction of the hot spot temperature. In response, this study establishes a methodology through which a thermal model of a HEMT can be developed to include accurate phonon relaxation times and multiscale effects. The Lattice Boltzmann (LB) discretization scheme of the BTE is utilized to include the elements of the phonon dispersion that must be ignored otherwise. To address concerns about realistic boundary conditions the LB model has been coupled to a Fourier finite difference scheme. This coupling overcomes some basic computational limits and therefore allows nanoscale phenomena to be resolved in a macroscopic domain.