We have determined the main parameters of the quasi-one-dimensional excitons confined in GaAs V-shaped quantum wires, namely exciton Bohr radius and binding energy, by two-photon absorption and magnetoluminescence experiments. The experimental results are in excellent agreement with our calculations, based on realistic wave functions for the actual wire geometry.

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Epitaxial GaN layers grown on sapphire contain a very large density of defects (threading dislocations, stacking faults, inversion domain boundaries, . . .). Among these defects, we have performed the analysis of the basal stacking faults by high resolution transmission electron microscopy. Two faults, I1 and I2, were identified. The formation of the I1 fault is based on the climb-dissociation process of the (1/3)⟨11-20⟩ or of the [0001] perfect dislocations whereas the I2 fault is due to the shear of the structure leading to a partial dislocation loop.

Despite the development of high-resolution electron microscopy (HREM) that allows imaging of most materials, the extraction of quantitative information at atomic scale still requires considerable additional efforts. This review presents the recent developments on techniques that can be used to determine the local strain, chemical composition or atomic structure retrieval in HREM. The source of noise in images and effective methods for improving the signal-to-noise ratio in direct or Fourier space are discussed. The artefacts of filtering are commented. In all the methods, the sample thickness has to be determined. A detailed analysis of the thin foil relaxation effect on the measured distortion fields is presented as well as the possibilities of using finite element calculations for its modelling. The local composition measurement based on the chemically sensitive reflections; pattern recognition and the measurement of lattice parameters are described. Examples from semiconductor heterostructures are discussed. The current state of the strategies used for the retrieval of the atomic configuration of defects from HRTEM images is briefly presented. The limits of detection and the accuracy of the methods are summarised; and it is pointed out that electron holography, focal series reconstruction and the coming Cs corrected microscopes will help to obtain this information with better accuracy. Content

The authors report on the plasma-assisted molecular-beam epitaxy of semipolar AlN(112¯2) films on (11¯00) m-plane sapphire. AlN deposited on m sapphire settles into two main crystalline orientation domains, AlN(112¯2) and AlN(101¯0), whose ratio depends on the III/V ratio. The in-plane epitaxial relationships of AlN(112¯2) on m-plane sapphire are [112¯3¯]AlN‖[0001]sapphire and [11¯00]AlN‖[112¯0]sapphire. In the case of AlN(101¯0), the in-plane epitaxial relationships were [12¯10]AlN‖[0001]sapphire and [0001]AlN‖[112¯0]sapphire. Growth under moderate nitrogen-rich conditions enables them to isolate the (112¯2) orientation and to improve the surface morphology of the layers.