Transmission electron microscopic, scanning electron microscopic, cathodoluminescence and photoluminescence studies were performed on a 30nm-GaN/2nm-In0.28Ga0.72N/2μm-GaN/(00•1) sapphire single quantum well sample. Scanning electron microscope
cathodoluminescence studies were performed at about 8K, using an optimum accelerating voltage of 4 to 6kV in order to maximize the quantum well luminescence. The cathodoluminescence in the vicinity of characteristic so-called V-shaped pits was investigated. Near band-edge luminescence maps from the GaN showed bright rings within the boundaries of the pits, while quantum-well luminescence maps showed the pits to be regions of low intensity. These observations were consistent with transmission electron microscopic observations which revealed the absence of quantum-well material in the pits. Variations in the band-edge and quantum-well maps in the regions between the pits were attributed to threading edge dislocations. The cathodoluminescence and photoluminescence quantum-well luminescence was observed to blue-shift and broaden with increasing excitation intensity. This was accompanied by a decreasing spatial resolution of the cathodoluminescence quantum-well maps; thus implying an increasing carrier diffusion length in the InGaN layer. It was suggested that screening of the piezoelectric field of the material could account for the observations.

Luminescence Studies of Defects and Piezoelectric Fields in InGaN/GaN Single Quantum Wells. S.J.Henley, A.Bewick, D.Cherns, F.A.Ponce: Journal of Crystal Growth, 2001, 230[3-4], 481-6