Yellow and blue luminescence in undoped GaN layers with different resistivities were studied by cathodoluminescence. Intense yellow and blue luminescence bands were observed in semi-insulating GaN, while in n-GaN the yellow luminescence and blue luminescence bands were very weak. The stronger yellow and blue luminescences in semi-insulating GaN were correlated to the higher edge-type dislocation density. The scanning cathodoluminescence image revealed strong defect-related luminescence at the grain boundaries where the dislocations accumulate. It was found that the relative intensity of the blue luminescence band to the yellow luminescence band increased with the cathodoluminescence beam energies and was larger in n-GaN with a lower density of edge-type dislocations. An approximately 3.35eV shoulder next to the near-band-edge peak was observed in n-GaN but not in semi-insulating GaN. A red-shift of the near-band-edge peak with cathodoluminescence beam energy was observed in both samples and was explained by internal absorption.

Cathodoluminescence of Yellow and Blue Luminescence in Undoped Semi-Insulating GaN and n-GaN. Q.F.Hou, X.L.Wang, H.L.Xiao, C.M.Wang, C.B.Yang, H.B.Yin, J.M.Li, Z.G.Wang: Chinese Physics Letters, 2011, 28[3], 037102