Spatially resolved cathodoluminescence (CL) spectrum mapping revealed a strong exciton localization in InGaN single-quantum-wells (SQWs). Transmission electron micrographs exhibited a well-organized SQW structure having abrupt InGaN/GaN heterointerfaces. However, comparison between atomic force microscopy images for GaN-capped and uncapped SQWs indicated areas of InN-rich material, which are about 20 nm in lateral size. The CL images taken at the higher and lower energy side of the spatially integrated CL peak consisted of emissions from complementary real spaces, and the area was smaller than 60 nm in lateral size. ©1997 American Institute of Physics.