Confocal microscopy and spectroscopy of InGaN epilayers on sapphire

We report a preliminary investigation of spatial inhomogeneities in an InGaN epilayer using scanning confocal microscopy as the investigative tool. The Daresbury confocal microscope SYCLOPS provides simultaneous high quality reflection and fluorescence images of InGaN sample areas up to 500 μm square, even at room temperature. Sample cooling increases the brightness and quality of the fluorescence image, as expected. Spectral selection using interference filters permits identification of features close to sample edges resulting from the nitridation of indium droplets. The unexpected non- coincidence of fluorescence and reflection features below 10 μm in size is tentatively attributed to the differing absorption strengths of different crystallites.