Two strain relaxation processes have been observed in AGaN layers grown on thick AlN templates. In Process I, a-type threading dislocations (TDs) with b= 1/3<1120> from the AlN underlayer are inclined away from the [0001] axis toward the <1100> directions when they enter the AlGaN film, forming dislocation line projection perpendicular to the Burger vector. In Process II, a+c-type TDs from the AlN underlayer with Burgers vector of b= 1/3<1123> glide on {0111} planes when they enter the AlGaN film to generate interfacial misfit dislocations lying along the <2110> directions at the AlGaN/AlN interface.

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We report on a new technology for growing low‐dislocation‐density AlGaN in which a Mg‐doped AlN underlying layer is used. By growing AlxGa1‐xN on AlN:Mg with AlN molar fractions x of 0.3, 0.5 and 0.7, the density of misfit dislocations is much reduced compared with that in the case of growing AlGaN on undoped AlN. In addition, the surface becomes atomically flat. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The special pair of the bacterial photosystem has been modeled with a porphyrin dimer (the partial structure is shown). As with the natural system, only one pyrrole ring from each monomer subunit participates in π overlap.

This paper reports the microstructural analysis of 20‐μm‐thick Al0.5Ga0.5N with improved crystalline quality owing to the use of a Mg‐doped AlN underlying layer. The threading dislocation density in 20‐μm‐thick Al0.5Ga0.5N on Mg‐doped AlN was 8.6×108cm‐2, which is about one‐fifth lower than that of Al0.5Ga0.5N on an undoped AlN underlying layer. The microstructural analysis was carried out to clarify dislocation behaviours in the Al0.5Ga0.5N layer on the Mg‐doped AlN underlying layer. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)