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

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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.
2012-10-25