Transmission electron microscopy (TEM), cathodoluminescence in the scanning electron microscope (SEM-CL) and photoluminescence (PL) studies were performed on a 30 nm GaN/2nm In0.28Ga N-0.72/2 mum GaN/(0 0 0 1) sapphire single quantum well (SQW) sample. SEM-CL was performed at low temperatures approximate to 8 K, and at an optimum accelerating voltage, around 4-6 kV to maximise the quantum well (QW) luminescence. The CL in the vicinity of characteristic "V-shaped" pits was investigated. The near band edge (BE) luminescence maps from the GaN showed bright rings inside the boundaries of the pits while the QW luminescence maps showed pits to be regions of low intensity. These observations are consistent with TEM observations showing the absence of QW material in the pits. Variations in both the BE and QW maps in the regions between the pits are ascribed to threading edge dislocations. The CL and PL QW luminescence was observed to blue-shift and broaden with increasing excitation intensity. This was accompanied by decreasing spatial resolution in the CL QW maps implying an increasing carrier diffusion length in the InGaN layer. The reasons for this behaviour are discussed. It is argued that screening of the piezoelectric field in the material may account for these observations.