We investigated the degradation of cleaved facets of (Al,In)GaN laser diodes in different atmospheres. We found that operation in water-free atmospheres with sufficient oxygen shows a slow degradation. Operation in atmospheres with water vapor causes a fast degradation and an oxidation on the facet. This deposition is a permanent damage to the laser diode. If the laser diode is operated in pure nitrogen, we find a thick deposition on the facet, which shows high absorption. This deposition can be removed by either high optical output powers or by operation in atmospheres with sufficient oxygen. We also explain the influence of these coatings to the degradation behavior and see these coatings as the reason for unstable kinks in the L–I characteristics during operation.

In this work we present degradation studies of GaN based blue‐violet laser diodes grown on different substrates. By replacing the SiC substrate by GaN substrate, we change from hetero to homo epitaxy, while the threading dislocation density (TDD) is reduced by 3 orders of magnitude. A detailed analysis of small signal I –V curves shows an increase of non radiative (NR) recombination centers during aging for laser diodes on SiC substrate. This was not observed for lasers on GaN substrate due to the reduced TDD and therefore reduced number of diffusion channels for Mg‐atoms, acting as NR recombination centers in the active region. With an improved epitaxial structure on GaN substrate, we increased the lifetime of our lasers by a factor of 10. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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We present a process for high quality InGaN laser diodes on free standing GaN substrates with high reproducibility. We demonstrate a self‐aligned process to contact lasers with ridge width <2 μm. The stability of the process allows us to optimize the epitaxial structure on GaN substrates and we achieve cw‐threshold current densities of 2.9 kA/cm2 for 10 μm wide ridges and 4.7 kA/cm2 for 1.5 μm wide ridges. Cw‐slope efficiencies of 1.0 W/A are achieved for both widths. Beside this we notice a reduction of the ideality factor and the forward bias linked to an improvement of the epitaxial interfaces. For maximum optical output we could achieve 3.4 W from one output facet at pulsed operation and a catastrophic optical mirror damage (COMD) level of 67 MW/cm2. Furthermore we observe a dependency of the COMD level from the pulse width corresponding to filament formation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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