Low dislocation density, high power InGaN laser diodes
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Internet Journal Nitride Semiconductor Research
Low dislocation density, high power InGaN laser diodes Piotr Perlin 1, M. Leszczy˜ski1, P. Prystawko1, P. Wisniewski1, R. Czernetzki1, C. Skierbiszewski1, G. Nowak1, W. Purgal1, J. L. Weyher1, G. Kamler1, J. Borysiuk1, M. Krysko1, M. Sarzynski1, T. Suski1, E. Litwin-Staszewska1, L. Dmowski1, G. Franssen1, S. Grzanka1, T. Swietlik1, I. Grzegory1, M. Bockowski1, B. Lucznik1, S. Porowski1, L Gorczyca3, A. Bering2, W. Krupczynski2, I. Makarowa2, R. Wisniewska2 and A. Libura2 1High
Pressure Research Center, Limited, 3AGH University of Technology, 2TopGaN
(Received Tuesday, December 16, 2003; accepted Wednesday, March 17, 2004)
We used single crystals of GaN, obtained from high-pressure synthesis, as substrates for Metalorganics Vapor Phase Epitaxy growth of violet and UV laser diodes. The use of high-quality bulk GaN leads to the decrease of the dislocation density to the low level of 105 cm-2, i.e. two orders of magnitude better than typical for the Epitaxial Lateral Overgrowth laser structures fabricated on sapphire. The low density and homogeneous distribution of defects in our structures enables the realization of broad stripe laser diodes. We demonstrate that our laser diodes, having 15 µm wide stripes, are able to emit 1.3-1.9 W per facet (50% reflectivity) in 30 ns long pulses. This result, which is among the best ever reported for nitride lasers, opens the path for the development of a new generation of high power laser diodes.
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Introduction
The most challenging problem for the realization of high power GaN/InGaN/AlGaN lasers is the very high density of threading dislocations present in epitaxial layers and device structures [1]. These dislocations result from the lattice mismatch between sapphire or SiC substrates and nitride overlayers. Due to the advancements in epitaxial technology, in particular in lateral overgrowth techniques (ELOG, PENDEO, FIELO) [2], it has been possible to lower the density of dislocations to the level of roughly 107 cm-2. However, in such structures, in spite of their sophistication, one can still find tens or hundreds of dislocations in the active area of typical laser diodes. The situation becomes even worse in case of wide stripe laser diodes. These lasers suffer from an increased number of defects within their active layer and, moreover, are difficult to manufacture because the standard ELOG techniques leave only narrow regions on the wafer with lowered dislocation density. These regions are usually too narrow to contain broader (15-50 µm) stripes. Since the lifetime of GaN/InGaN/AlGaN lasers is directly related to the density of dislocations in the material [3], the only way to produce fully reliable devices is to a use
qualitatively better substrate material. A new path was paved recently by a Japanese company – Sumitomo, which succeeded in producing high quality GaN layers characterized by a dislocation density of the order of 105-106cm-2. By using their proprietary FIELO-like technology called “DEEP” (dislocation elimina
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