Near-field photoluminescence spectroscopy of InGaN films grown by molecular-beam epitaxy

The spatial and spectral distribution of photoluminescence from InGaN films grown by plasma-assisted molecular-beam epitaxy are studied by near-field scanning optical microscopy. The luminescence intensity is low in the vicinity of pits in the surface that are believed to be associated with dislocations. For 20% In, the emission is random on a submicron length scale, but clumps into micron-sized regions at 27% In. The clustering is quantified by calculating the image entropy. Near-field spectra indicate that the regions of high intensity are not due to a local increase in In. Spatial variations in the luminescence wavelength indicate that composition fluctuations are enhanced with increasing In.