Two‐Mode and Disorder‐Induced Phonon Features in Al _<i>x</i> In _{1– <i>x</i>} N Films

Phonon mode assignments of the E 2 (high) and A 1 (LO) modes in wurtzite Al x In 1– x N alloy films with x = 0–0.18 are systematically investigated using micropolarized Raman scattering. The identification of phonon modes is accomplished through detailed analyses of their peak positions, linewidths, intensity ratios, and polarization characteristics. As the Al molar fraction x increases, both the E 2 (high) and A 1 (LO) modes exhibit moderate shifts toward higher frequencies and peak broadening, which indicate alloying effects and increased lattice disorder. The variation of the E 2 (high) peak frequency shows good agreement with theoretical predictions based on the modified random element isodisplacement model, confirming its two‐mode behavior. The pure A 1 (LO) mode was successfully extracted under the cross‐polarized configuration, and its frequency evolution clearly demonstrates two‐mode characteristics consistent with previous experimental results. In addition to these principal phonon modes, Raman‐forbidden B 1 vibrations and phonon density of states–related features were newly observed, attributed to alloy‐induced mass and force constant fluctuations between AlN and InN. These findings provide new insights into phonon dynamics in III‐nitride ternary alloys and are expected to stimulate further discussion bridging theoretical and experimental perspectives.