ABSTRACT
Gallium nitride based structures have been characterised using the novel approach of simultaneous wavelength-dispersive X-ray microanalysis and cathodoluminescence spectral mapping. Application of the technique to metalorganic vapor phase epitaxy-grown indium gallium nitride epilayers shows microscopic variations in the indium content, which correlate directly with spatially-dependent shifts observed in the peak wavelength of the luminescence spectrum. Some questions concerning the origin of this luminescence and its precise relationship with the indium content, in particular with regard to the roles of indiumrich quantum dots and piezoelectric fields, and even the value of the fundamental bandgap oflnN itself. Thallium acid phthalate and pentaerythritol crystals were used to select the La X-ray lines from gallium and indium respectively. The elemental maps of indium and gallium show many similar contrast features which, by comparison with the backscattered electron image, can be identified as resulting from the surface roughness.
