Spatial distribution of yellow luminescence related deep levels in GaN

Using two-photon excitation, we study the excitation power density dependence and spatial variation of photoluminescence (PL) in GaN films grown by molecular beam epitaxy. Under our experimental conditions, the excitation power density dependence is quadratic for near band-gap emission (NBE) and linear for yellow luminescence (YL), consistent with the YL process being saturated. The PL mapping reveals NBE fluctuations at the domain-size scale while YL is uniform. These results provide strong evidence that the spatial distribution of deep levels associated with YL is uniform; hence, YL is unrelated to dislocations. (C) 2003 American Institute of Physics.