Nanoscopic Photoluminescence Properties of a Green-Emitting InGaN Single Quantum Well on a $\{20\bar{2}1\}$ GaN Substrate Probed by Scanning Near-Field Optical Microscopy

Nanoscopic photoluminescence (PL) properties of a green-emitting $\{20\bar{2}1\}$ InGaN single quantum well (SQW) are investigated by scanning near-field optical microscopy (SNOM). Carrier/exciton diffusion outside the probe aperture of 150 nm is demonstrated by a multimode SNOM technique. The estimated diffusion lengths are ${\sim}70$ nm along the [$\bar{1}014$] direction and ${\sim}50$ nm along the [$\bar{1}2\bar{1}0$] direction, and are in between those of ($11\bar{2}2$) and (0001) InGaN QWs. This finding is well accounted for by the difference in carrier/exciton lifetimes. Furthermore, atomic force microscopy (AFM) reveals ridge structures along the [$\bar{1}2\bar{1}0$] direction. Superimposing the SNOM-PL image with an AFM image, we find a clear correlation between the spatial distributions of PL peak wavelength and surface morphology.