Inhomogeneity of a highly efficient InGaN based blue LED studied by three-dimensional atom probe tomography

The InGaN based multiple quantum well (MQW) structure in a commercially available white light emitting diode (LED) was studied by transmission electron microscopy (TEM) and three-dimensional atom probe tomography (APT). The average In mole fraction by three-dimensional (3D) APT was found to be about 18% in the InGaN well which is consistent with the secondary ion mass spectrometry (SIMS) analysis. The In distribution in the InGaN well layer was analyzed by the iso curve mapping of 3D APT and found to be non-uniform in the InGaN active layer In clustering or In rich regions in the range of 2-3 nm size were found, in contrast to recent reports. Our results thus indicate that In clustering is essential for high-brightness InGaN based LEDs. We have also observed a discontinuity in the range of 50-100. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim