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Microcomposition and luminescence of InGaN emitters

Martin, R.W. and Edwards, P.R. and O'Donnell, K.P. and Mackay, E.G. and Watson, I.M. (2002) Microcomposition and luminescence of InGaN emitters. Physica Status Solidi A, 192 (1). pp. 117-123. ISSN 1862-6300

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Abstract

Using wavelength dispersive X-ray (WDX) spectrometers on an electron probe micro-analyser (EPMA) the indium content of a number of homogeneous and inhomogeneous InGaN epitaxial layers has been accurately mapped. The addition of a spectrometer and silicon CCD array to the light microscope, which shares the same focus as the electron microscope, enables cathodoluminescence spectra to be collected from exactly the same spot as sampled by the WDX spectrometers. As a result the dependencies of the luminescence energy and linewidth on the local indium nitride fraction can be investigated with greater confidence than in earlier reports, where separate measurements of luminescence and composition were required. Samples studied have indium nitride fractions ranging from <0.01 to approximately 0.25, corresponding to luminescence peaks covering the ultraviolet, blue and green regions of the spectrum. A linear dependence of luminescence peak energy on indium fraction is demonstrated and the linewidth variation plotted. Secondary electron images recorded in the EPMA reveal a wide range of topographies, varying from coalesced micrometre-scale hexagonal crystallites to densely packed layers.