Controlling the yellow luminescence intensity from n-GaN during cathodoluminescence

GaN grown on sapphire by hydride vapour phase epitaxy is probed by ion channeling, Raman and cathodoluminescence (CL) spectroscopy. Channeling and Raman spectroscopy indicate that the quality of GaN is very good. Spot mode CL measurement signifies intense near band edge emission as compared with yellow luminescence (YL). During scanning over an area, the YL intensity could be controlled by the electron beam dwell time (DT). The YL intensity decreases with the increase of DT and saturates beyond a threshold value due to overexposure of a given pixel leading to non-radiative emission. But for shorter dwell times repeated excitations of a given pixel increase the intensity of YL. These results may be explained invoking the decay time and density of defects responsible for YL. Control over YL intensity will be useful for assessing low defect concentrations, their origin and also to increase spatial resolution of CL measurements on nanostructures.