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(In,Ga)N

Currently, the luminous efficacy of LEDs in the green spectral range is low compared to that of red or blue LEDs. This "green gap" has undesirable consequences for applications such as illumination or backlighting of displays. There are thus world-wide efforts to fabricate high In content (In,Ga)N/GaN quantum wells of high crystal quality. The comparatively low growth temperature of MBE may facilitate the incorporation of a large fraction of In while retaining a homogeneous material.

(In,Ga)N is a fascinating, but complex material both from the view of growth and spectroscopy.[1] The coexistence of internal electrostatic fields and exciton localization complicates the analysis of the optical spectra as well as of the recombination dynamics.[2] Indium surface segregation may severely distort the composition profiles of (In,Ga)N/GaN quantum wells with dramatic consequences for the transition energy and the luminescence decay time.[3,4] We use a variety of spectroscopic techniques, particularly µ-photoluminescence and cathodoluminescence, to investigate this material and to obtain information of its spatially resolved composition and spectral emission.

The example shows the superposition of a monochromatic cathodoluminescence image and a scanning electron micrograph of an (In,Ga)N layer. In the center of each intensity minimum, a dislocation intersecting the surface is clearly visible.

InGaN micrograph
 

  1. O. Brandt and K. H. Ploog, The benefit of disorder, Nature Mater. 5, 769 (2006).
  2. P. Waltereit, O. Brandt, J. Ringling, and K. H. Ploog, Electrostatic fields and compositional fluctuations in (In,Ga)N/GaN multiple quantum wells grown by plasma-assisted molecular beam epitaxy, Phys. Rev. B 64, 245305 (2001).
  3. P. Waltereit, O. Brandt, K. H. Ploog, M. A. Tagliente, and L. Tapfer, In surface segregation during growth of (In,Ga)N/GaN multiple quantum wells by plasma-assisted molecular beam epitaxy, Phys. Rev. B 66, 165322 (2002).
  4. O. Brandt, Y. J. Sun, H.-P. Schönherr, K. H. Ploog, P. Waltereit, S.-H. Lim, and J. S. Speck, Improved synthesis of (In,Ga)N/GaN multiple quantum wells by plasma-assisted molecular beam epitaxy, Appl. Phys. Lett. 83, 90 (2003).

 

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