Compositional pulling effects in InxGa1_xN/GaN layers: a combined depth-resolved cathodoluminescence and Rutherford backscattering/channeling study

S. Pereira, M. R. Correia, E. Pereira, K. P. O'Donnell, C. Trager-Cowan, F. Sweeney, E. Alves

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Abstract

A depth-resolved study of the optical and structural properties of wurtzite InGaN/GaN bilayers grown by metallorganic chemical vapor deposition on sapphire substrates is reported. Depth-resolved cathodoluminescence (CL) and Rutherford backscattering spectrometry (RBS) were used to gain an insight into the compositional profile of a 75-nm thick InGaN epilayer in the direction of growth. CL acquired at increasing electron energies reveals a peak shift of about 25 meV to the blue when the electron beam energy is increased from 0.5 to ∼7 keV, and shows a small shift to lower energies between ∼7 and 9 keV. For higher accelerating voltages the emission energy peak remains constant. This behavior can be well accounted for by a linear variation of In content over depth. Such an interpretation conforms to the In/Ga profile derived from RBS, where a linear decrease of the In mole fraction from the near surface (∼0.20) down to the near GaN/InGaN interface (∼0.14) region fits the random spectra very well. Furthermore, by measuring the tetragonal distortion at different depths, using RBS/channeling, it is shown that regions of higher In content also appear to be more relaxed. This result suggests that strain hinders the incorporation of In atoms in the InGaN lattice, and is the driving force for the compositional pulling effect in InGaN films.

Original languageEnglish
Article number205311
Number of pages5
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume64
Issue number20
DOIs
Publication statusPublished - 15 Nov 2001

Keywords

  • cathodoluminescence
  • sapphire substrates
  • InGaN lattice

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