Phonon Scattering by Dislocations in GaN

Crystal imperfections such as dislocations strongly influence the performance and thermal transport behavior of GaN-based devices. We show that the experimental data used to parametrize the effect of dislocations on the thermal conductivity can be explained using only the reported film thickness and point defect concentrations. The analysis highlights the boundary-scattering-governed reduction of thermal conductivity in GaN, which had been underestimated in earlier models. To quantify the influence of dislocations on the thermal transport in GaN, we adopt a Green's function approach based on accurate ab initio interatomic force constants. While calculations at the level of density functional theory are necessary for three-phonon and point defect scattering, we show that scattering due to dislocations can be satisfactorily approximated using semiempirical potentials. This makes the Green's function approach to dislocation scattering a quantitatively predictive, yet computationally practical, method for obtaining detailed phonon scattering rates.