Direct observation of large-scale nonuniformities in hydride vapor-phase epitaxy-grown gallium nitride by cathodoluminescence

Hydride vapor phase epitaxial GaN films grown on sapphire without a buffer are found to contain large-scale regions with high electron concentration located close to the interface. These regions are composed of individual columns forming an irregular but quasicontinuous layer, while the rest of the film has a much lower carrier concentration. The highly doped regions are easily visualized using cathodoluminescence. The coexistence of regions with low and high electron concentration allows us to explain the concurrent evidence of high film quality in photoluminescence, Raman spectroscopy and x-ray diffraction, and a high electron concentration measured in transport studies. (C) 1998 American Institute of Physics. [S0003-6951(98)03850-9].