In this work we present a study on the influence of an in situ grown SiNx intermediate layer inside (Al)GaN epitaxial layers grown on SiC substrates on dislocation densities and material strain of the epitaxial films. A defect density of 6×108cm-2 was achieved by reducing the number of pure edge dislocations in the order of one magnitude. It was found that a reduction of the dislocation density is only successful by inserting the SiNx layer inside GaN films and no defect reduction takes place with SiNx inside AlGaN films. The presence of stacking faults at the close vicinity of the SiNx layer plays an important role for the mechanism of dislocation termination at the SiNx interface. To determine dislocation densities an etch pit density method was carried out combining transmission electron microscopy (TEM) investigations of plan-view samples with atomic force microscopy (AFM) scans. Structural properties were investigated by cross-sectional TEM samples. Composition of AlGaN at the SiNx interface was determined by energy dispersive X-ray analysis (EDX) and secondary ion mass spectroscopy (SIMS). Material strain was investigated by micro-photoluminescence measurements (μ-PL).

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 tan. 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/cm(2) for 10 mu m wide ridges and 4.7 kA/cm(2) for 1.5 mu m 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/cm(2]). Furthermore we observe a dependency of the COMD level from the pulse width corresponding to filament formation. (c) 2006 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.

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 dislocaton 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. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

We present a novel modified technique of in situ etching with tertiarybutyl chloride (TBCl) which allows etching of both, GaInAsP/InP and AlGaInAs/InP structures for the fabrication of buried heterostructure (BH) lasers in an MOVPE system. It is shown that the surface morphology is improved, when small amounts of trimethyl gallium are injected during TBCl etching at reduced reactor pressure. The etching process is performed in a PH3-free atmosphere under hydrogen. Therefore, the etching temperature has to be kept at the relatively low value of 580°C. GaInAsP and AlGaInAs MQW laser ridges can be formed by in situ etching under identical reactor conditions (pressure, temperature, precursor flow). For Al containing layers, however, an ex situ wet chemical etch dip is additionally required in order to avoid residue deposition which results in deteriorated surface morphology. High-quality GaInAsP and AlGaInAs ridges for BH laser applications are obtained. GaInAsP/InP BH lasers fabricated by this technique exhibit excellent high-temperature characteristics.

SUMMARY Technological forecasting is located in technological space for a certain engineering domain and is the first step in the research and development of a new technology. There are many techniques already developed for technological forecasting like extrapolation of trends, heuristics forecasting by expert e.g. Delphi method, etc. The morphological method (MM) is used to describe a technique for identifying, indexing, counting and parametrizing the collection of all possible devices to achieve a specified functional capability. This is not a forecasting per se, but it is a useful organizing tool, a source of insights, and a starting point for further analysis by other methods, Milačić (1976). In the paper we expand the capabilities of MM using artificial intelligence (Al) principles. The AI production system has a global data base, a set of production rules and a control system. Special attention is paid to control strategy-developing searching techniques in order to distinguish the explicit local knowledge about how to proceed toward a goal from any state from the implicit global knowledge of the complete solution. Some practical examples are also shown.