Plan-view transmission electron microscopy (TEM) and cathodoluminescence (CL) images were taken for the same sample at exactly the same location in n-type GaN grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD). There was a clear one to one correspondence between the dark spots observed in CL images and the dislocations in TEM foils, indicating that the dislocations are non-radiative recombination centers. The hole diffusion length in n-type GaN was estimated to be neighboring 50 nm by comparing the diameters of the dark spots in thick samples used for CL and samples that were thinned for TEM observation. The efficiency of light emission is high as long as the minority carrier diffusion length is shorter than the dislocation spacing.

The role of dislocation for luminescence in InGaN grown on sapphire substrate by metal organic chemical vapor deposition (MOCVD) method was investigated by cathodoluminescence (CL) and atomic force microscopy (AFM). The CL emission area and dark spots between InGaN and GaN layers in InGaN/GaN single quantum well (SQW) and multiple quantum well (MQW) structures showed completely one to one correspondence. These results indicate that dislocations in InGaN work as non-radiative recombination centers. Furthermore it was confirmed that the phase separation in InGaN is caused by spiral growth due to mixed dislocations, and such a growth mechanism is discussed.

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