Evidence for phonon-plasmon interaction in InN by Raman spectroscopy

The interaction between carriers and polar phonons in InN is investigated using Raman spectroscopy. An irreversible broadening and redshift of the 595 cm^-1 A₁(LO)-like phonon mode, observed after annealing the layer to 700K, is direct evidence of phonon-plasmon interaction in InN. Variable field Hall effect measurements reveal that the 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 A₁(LO)-like mode broadening is related to surface conduction carriers.