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Electron microscopy techniques are applied to investigate structural properties of GaN layers selectively grown by hydride vapor phase epitaxy on crystalline and amorphous GaN seed layers deposited on (0001)Al2O3 substrates. Optimalization of the growth conditions lead to a reduction both of the stacking fault concentration and c-axis tilting in the laterally grown regions. During the lateral growth threading dislocations from the seed layer bend from vertical direction of propagation. Bending behavior depends on the type of the dislocation and on the shape of the GaN film in the initial stage of the growth. Optical properties of laterally grown regions are correlated with the high point-defect incorporation that is revealed by high-resolution electron microscopy.

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Summary. --Photoluminescence (PL) and electroluminescence (EL) measurement of GaAs/A1GaAs quantum ~res (QWR) located in the active region of a p-i-n junction are reported. The samples are fabricated by molecular-beam epitaxial growth on V-grooved substrates. Good control of the interface, defect density and doping profile have been achieved. Homogeneous current injection into the quantum wires is achieved with efficiencies comparable to current injection into a quantum well control sample. PL with and without an applied voltage across the junction was measured at 86 K and 300 K for different excitation densities. Peaks appearing with an applied voltage correspond to the active-region QWR transitions and are also observed on the EL spectra measured at 120 K and at 300 K. Clear evidence of 1D confinement is observed in both PL and EL spectra. They show a one-'dimensional splitting of about 24 meV and a saturation of the ground state at high excitation density. The polarisation of the PL and EL is in good agreement with the expected anisotropy of the 1D matrix elements. PACS 73.20 -Surface and interface electron states. PACS 01.30.Cc -Conference proceedings.