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Room temperature ferromagnetism of GaMnN thin film is awaked by a mild hydrogenation treatment of a sample synthesized by molecular beam epitaxy. Local environment of Mn atoms is monitored by Mn-L2,3 near edge x-ray absorption fine structure technique. Doped Mn ions are present at substitutional sites of Ga both before and after the hydrogenation. No secondary phase can be detected. Major valency of Mn changes from 3+ to 2+ by the hydrogenation. The present result supports the model that the ferromagnetism occurs when Mn2+ and Mn3+ are coexistent and holes in the midgap Mn band mediate the magnetic coupling. [ABSTRACT FROM AUTHOR]

InN with a film thickness of 600 nm was grown on a (0 0 0 1) sapphire substrate using low-temperature-grown intermediate layers by radio frequency plasma-excited molecular beam epitaxy (RF-MBE). From SEM observation, it was found that InN films with uniform surface morphology were grown. The electron mobility at room temperature obtained in this study was 830 cm2/V s and the corresponding carrier density was 1.0×1019 cm-3. To our knowledge, this electron mobility is the highest value ever reported for single-crystal InN films. [Copyright &y& Elsevier]

GaN films were grown at various V/III ratios on sapphire (0 0 0 1) substrates with and without nitridation process by radio-frequency plasma-excited molecular beam epitaxy. Based on the results of X-ray diffraction pole-figure and φ scan measurements, the GaN film grown without nitridation process has a tendency to form the metastable in-plane rotation domain by ∼11° from the substrate, in addition to the main domain rotated by 30° from the substrate. In suppressing the formation of the metastable in-plane rotation domain, it is found to be very effective to perform the nitridation process. In addition, even in GaN films grown without nitridation process, decrease in V/III ratio enables us to suppress the formation of the metastable domain. The rotation domains are considered to have the epitaxial relationship of [1 2 &3macr; 0]GaN||[1 1 &2macr; 0]sapphire and [&1macr; &2macr; 3 0]GaN||[1 1 &2macr; 0]sapphire. [Copyright &y& Elsevier]

We investigate the effect of hydrogen on morphological changes in GaN columns grown by electron–cyclotron-resonance plasma-excited molecular beam epitaxy on sapphire (0 0 0 1) substrates. In GaN growth with a hydrogen flow of 6 sccm, hexagonal columnar structure was obtained. Morphological changes of the GaN columns from hexagonal to triangle were observed by increasing the hydrogen flow rate. It is considered to be caused by preferential growth along three of the six 〈1 0 &1macr; 0〉 directions. The surface of the triangle columns consisted of {1 0 &1macr; 3} and {1 0 &1macr; 1} faceted planes. Formation mechanism of the triangle columnar structure is discussed. [Copyright &y& Elsevier]

Abstract: High-quality epitaxial InN films have been employed as underlying templates for the growth of In-rich In x Ga1− x N (0.71⩽x⩽0.90) films by radio-frequency plasma assisted molecular beam epitaxy. The epitaxial InN films (InN templates) with the thickness of 500nm were grown on (0001) sapphire substrates with a low-temperature deposited 10nm thick InN (LT-InN) buffer layer, and then In-rich In x Ga1− x N films with the thickness of 250nm were grown on these InN templates. As compared with In-rich In x Ga1− x N films grown directly on the LT-InN buffer layers, the In-rich In x Ga1− x N films grown on the InN templates showed a decrease in full-width at half-maximum of the (0002) X-ray rocking curves. It was found that the insertion of the InN template was very effective in improving the crystalline quality of In-rich In x Ga1− x N. Optical properties were also investigated by photoluminescence. Lattice distortion of the In-rich In x Ga1− x N films induced by the underlying InN templates is also discussed. [Copyright &y& Elsevier]