The macroscopic polarization effect on thermal conductivity of binary nitrides

We theoretically investigate the effect of macroscopic polarization on phonon thermal conductivity of wurtzite (WZ) binary nitrides (AlN, GaN and InN). Our results show that macroscopic polarization contributes to the effective elastic constant of the wurtzite nitrides and modifies the phonon group velocity, Debye frequency, and Debye temperature. Using revised phonon velocity and Debye temperature, different phonon scattering rates and combined scattering rate are calculated as functions of the phonon frequency at room temperature. We estimate phonon thermal conductivity of binary nitrides using these modified parameters. The theoretical analysis shows that up to a certain temperature (different for AlN, GaN, and InN) the polarization effect acts as ill effect and reduces the thermal conductivity. However, after this temperature, the thermal conductivity is significantly enhanced by the polarization effect. The revised thermal conductivity at room temperature is found to be increased by 12% in GaN, 18% in InN and 20% in case of AlN due to macroscopic polarization, i.e., maximum polarization effect is observed in AlN and minimum in GaN. The method we have developed can be used for calculation of thermal energy in the active region of nitride optoelectronic devices.