The interaction between carriers and polar phonons in $\mathrm{InN}$ is investigated using Raman spectroscopy. An irreversible broadening and redshift of the $595{\mathrm{cm}}^{-1}$ $A_1\left(\mathrm{LO}\right)$-like phonon mode, observed after annealing the layer to $700\mathrm{K}$, is direct evidence of phonon-plasmon interaction in $\mathrm{InN}$. Variable field Hall effect measurements reveal that the $\mathrm{InN}$ layer is electrically heterogeneous and has at least three conduction layers exhibiting a reduction in mobility after annealing, consistent with the phonon-plasmon coupled mode broadening. A comparison between simulated and experimental coupled mode line shapes indicates that the mobility changes measured for bulk or interface carriers is not large enough to account for the experimentally observed annealing-induced broadening of the LO-like mode. We speculate that the observed $A_1\left(\mathrm{LO}\right)$-like mode broadening is related to surface conduction carriers.

• Received 6 March 2006

DOI:https://doi.org/10.1103/PhysRevB.75.035205