Nanoscale InN clusters and compositional inhomogeneities in InGaN epitaxial layers quantified by tip-enhanced Raman scattering

We investigate the compositional homogeneity of InGaN thin films with a high In content grown by migration-enhanced plasma-assisted metal-organic chemical vapor deposition. Micro-Raman spectroscopy and tip-enhanced Raman spectroscopy (TERS) are used to analyze the local InGaN composition on the micro- and nanoscale. Based on conventional micro-Raman mapping, the InGaN composition for all samples appears uniform but shows indications for intrinsic phase separations. TERS, a nanoscopic technique with a high spatial resolution far below the diffraction limit, verifies the formation of nanoscale compositional inhomogeneities. The dimensions of these compositional fluctuations observed in TERS are confirmed by scattering-type scanning near-field infrared nanoscopy (s-SNIN). In contrast to s-SNIN, we show that TERS furthermore enables the quantification of the In content in the different compositional regions and even allows the identification of InN nanoclusters near the surface of the epitaxial films