Microcathodoluminescence spectra, microcathodoluminescence imaging, electron beam induced current imaging, capacitance-voltage profiling, and deep-level transient spectrum measurements with optical injection were performed on 3µm-thick epilayers prepared by metal organic chemical phase deposition on top of thick free-standing GaN crystals grown by hydride vapour-phase epitaxy. The GaN substrates exhibited a dislocation density of about 5 x 106/cm2 near to the back surface and about 106/cm2 near to the Ga surface upon which the epitaxy was carried out. The dislocations were revealed as broad dark spots in microcathodoluminescence spectra from the (00▪1) surface, and as dark broad lines on the cleaved surface. The structure of the GaN film was more complicated, and exhibited a pattern of arrowhead-like features of alternating dark-bright contrast. Microcathodoluminescence spectra from the dark and bright regions indicated that the shallow donors in the dark region were more heavily compensated. The carrier lifetime near to defects was greatly reduced. The deep-level transient spectra measurements, with optical injection, of films revealed the presence of well-known hole traps with an activation energy of 0.85eV; often associated with the GaN yellow luminescence band.

Microcathodoluminescence and Electrical Properties of GaN Epitaxial Layers Grown on Thick Free-Standing GaN Substrates. A.V.Govorkov, N.B.Smirnov, A.Y.Polyakov, A.V.Markov, L.Voss, S.J.Pearton: Journal of Vacuum Science & Technology B, 2006, 24[2], 790-4