Structural and optical properties of InGaN/GaN layers close to the critical layer thickness

SERGIO MANUEL DE SOUSA PEREIRA, M.R. Correia, Eduarda Pereira, Carol Trager-Cowan, Francis Sweeney, Kevin O'Donnell, E. Alves, N. Franco, A.D. Sequeira

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In this work, we investigate structural and optical properties of metalorganic chemical vapor deposition grown wurtzite InxGa1−xN/GaN epitaxial layers with thicknesses that are close to the critical layer thickness (CLT) for strain relaxation. CLT for InxGa1−xN/GaN structures was calculated as a function of the InN content, x, using the energy balance model proposed by People and Bean [Appl. Phys. Lett. 47, 322 (1985)]. Experimentally determined CLT are in good agreement with these calculations. The occurrence of discontinuous strain relaxation (DSR), when the CLT is exceeded, is revealed in the case of a 120 nm thick In0.19Ga0.89N layer by x-ray reciprocal space mapping of an asymmetrical reflection. The effect of DSR on the luminescence of this layer is clear: The luminescence spectrum shows two peaks centered at ∼2.50 and ∼2.67 eV, respectively. These two components of the luminescence of the sample originate in regions of different strain, as discriminated by depth-resolving cathodoluminescence spectroscopy. DSR leads directly to the emergence of the second, lower-energy, peak. Based on this experimental evidence, it is argued that the appearance of luminescence doublets in InGaN is not evidence of “quantum dotlike In-rich” or “phase separated” regions, as commonly proposed.
Original languageEnglish
Pages (from-to)1207
Number of pages3
JournalApplied Physics Letters
Issue number7
Publication statusPublished - Jun 2002


  • indium compounds
  • gallium compounds
  • cathodoluminescence
  • semiconductor epitaxial layers


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