Theoretical study of built-in-polarization effect on relaxation time and mean free path of phonons in Al x Ga1−x N alloy

In this article we have investigated theoretically the effect of built-in-polarization field on various phonon scattering mechanisms in Al x Ga 1−x N alloy. The built-in-polarization field of Al x Ga 1−x N modifies the elastic constant, group velocity of phonons and Debye temperature. As a result, various phonon scattering mechanisms are changed. Important phonon scattering mechanisms such as normal scattering, Umklapp scattering, point defect scattering, dislocation scattering and phonon–electron scattering processes have been considered in the computation. The combined relaxation time due to above-mentioned scattering mechanisms has also been computed as a function of phonon frequency for various Al compositions at room temperature. It is found that combined relaxation time is enhanced due to built-in-polarization effect and makes phonon mean free path longer, which is required for higher optical, electrical and thermal transport processes. The result can be used to determine the effect of built-in-polarization field on optical and thermal properties of Al x Ga 1−x N and will be useful, particularly, for improvement of thermoelectric performance of Al x Ga 1−x N alloy through polarization engineering.