• Optical phonons of hexagonal ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}:$ Simulation and experiment

The behavior of longitudinal and transverse optical phonons in hexagonal ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ is derived theoretically and experimentally as a function of the concentration $\text{x(0⩽x⩽1).}$ The theoretical approach is based on a modified random element isodisplacement model which considers the interactions with the nearest neighbor and second neighbor atoms. We find “one-mode” behavior in ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ in which the phonon frequency in general varies continuously and approximately linearly with $\mathrm{x.}$ The theoretical simulations are in good agreement with Raman scattering experiments, which also reveal that both the linewidth and intensity of the optical phonons strongly depend on the concentration.