The structural investigation of the processed  InGaN/GaN LDs and LEDs structures are performed by the Transmission Electron Microscopy. A PEMBE process is used to fabricate laser structures on high pressure bulk GaN substrates [1]. The indium composition inside the active MQW region is measured by the analysis of the local lattice distortion using  high resolution HRTEM Images. The characterization of different types of structural defects of the structures is given in this paper.

The figures above show the cross-section of a laser structure with the top ohmic contact, after the   functional tests. Over the mesa region the remaining ZrO_x mask can be seen (figure a). Local lattice distortion maps in the active region of In_x1Ga_1-x1N/In_x2Ga_1-x2N MQW lasers (figure b) show high homogeneity of the indium composition along individual QWs, as well as between them. The low magnification TEM image (figure c) shows a part of the processed laser structure. The threading dislocations, which start at the interface between the bulk GaN and the Si doped GaN and the defects in the Mg doped top cladding are detected. These defects can be related to the discontinuities of the Ni layer. The local heating caused by the local non-uniform density of the current can be the origin of  this defect creation.

[1] C. Skierbiszewski, P. Winiewski, M. Siekacz, P. Perlin, A. Feduniewicz-Zmuda, G. Nowak, I. Grzegory, M. Leszczyski, and S. Porowski , Appl. Phys. Lett. 88, 221108 (2006).

The work was partially supported by the EU project ITN RAINBOW 213238-2

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