We describe the internal structure of acceptor-bound excitons in wurtzite semiconductors. Our approach consists in first constructing, in the context of angular momentum algebra, the wave functions of the two-hole system that fulfill Pauli's exclusion's principle. Second, we construct the acceptor-bound exciton states by adding the electron states in a similar manner that two-hole states are constructed. We discuss the optical selection rules for the acceptor-bound exciton recombination. Finally, we compare our theory with experimental data for CdS and GaN. In the specific case of CdS for which much experimental information is available, we demonstrate that, compared with cubic semiconductors, the sign of the short-range hole-exchange interaction is reversed and more than one order of magnitude larger. The whole set of data is interpreted in the context of a large value of the short-range hole-exchange interaction Xi(0)=3.4 +/- 0.2 meV. This value dictates the splitting between the ground-state line I-1 and the other transitions. The values we find for the electron-hole spin-exchange interaction and of the crystal-field splitting of the two-hole state are, respectively, -0.4 +/- 0.1 and 0.2 +/- 0.1 meV. In the case of GaN, the experimental data for the acceptor-bound excitons in the case of Mg and Zn acceptors, show more than one bound-exciton line. We discuss a possible assignment of these states.

By comparing a series of optical experiments performed on bulk aluminum nitride crystals and heteroepitaxial films, we determine the hydrostatic excitonic deformation potentials of AlN. The agreement between the whole available experimental data and our analysis consolidates this determination. Using the previously determined values of the valence-band deformation potentials which account for the strain-induced variation in the crystal-field splitting: d(3)=-8.19 eV and d(4)=4.10 eV we obtain values of -6.04 and 2.15 eV for the hydrostatic excitonic deformation potentials a(1) and a(2) in the context of the quasicubic approximation. This constitutes the first series of values coherent with the whole set of experimental data. The experimental value of 1s-2s splitting disagrees with the theory of excitons in anisotropic semiconductors. This disagreement, we attribute it to our poor knowledge of the valence-band dispersion relations of AlN and to the difficulty we face for including in the calculation plausible values for the anisotropic hole effective mass, dielectric constant.

By iteratively solving the Schrodinger and Poisson equations, we determine theoretical values of built-in electric field induced by spontaneous and piezoelectric polarizations in wurtzite CdxZn1-xO/ZnO (x <= 0.2) quantum wells (QWs) grown along < 0001 > polar direction. By adjusting recent photoluminescence data, we find that this internal field increases with x with a linear slope A = 17.83 MV/cm. Spontaneous and piezoelectric polarization variations are also determined together with the sheet charge densities at CdxZn1-xO/ZnO heterointerface. Our results indicate similar, but much stronger polarization effects than previously reported for MgxZn1-xO/ZnO QWs. They constitute record polarization effects ever reported for wide bandgap heterostructures, including group III-nitrides. (C) 2010 Elsevier Ltd. All rights reserved.

The Purcell effect, acceleration of a spontaneous emission recombination rate, has been observed in InN/In nanocomposites with buried nanoparticles of metallic In. This effect, associated with localized plasmons, is characterized by the averaged Purcell factor as high as 30-40 in the structures with large enough particles. This high value is indicative of a noticeable contribution from the emitting dipoles polarized normally to the nanoparticle surface in this system. The experimental observation of shortening of the emission lifetimes with increasing the amount of In is supported by calculations performed in a semiclassical approximation.

We have investigated the heteroepitaxial growth of indium nitride on sapphire substrates having different orientations. Growths were performed on C-, A-, M-, and R-plane-oriented sapphire in order to analyze the substrate orientation effect on the structural, optical, and electronic properties of InN. The orientation relationship between InN and sapphire was deduced by theta/2 theta High-resolution X-ray diffraction (HRXRD) measurements. These experiments show the ability to grow InN along nonpolar (11 (2) under bar0) orientation and the semipolar (11 (2) under bar2) orientation, depending of the orientations of the sapphire substrate. The crystalline quality was assessed by XRD symmetric and asymmetric rocking curve. measurements. We observed no drastic disparity between our samples, all exhibiting a reasonable crystalline quality. Atomic force microscopy imaging on these, layers, revealed different surface morphologies with a roughness varying between 30 and 60 nm. Electrical properties of the InN samples were investigated by room temperature Hall effbt.Cmeasourements and a line shape fitting of the photoluminescence was performed in order to get optically the values of the residual carrier density in the nitride layers. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Since a few years, indium nitride promising properties for device applications have attracted much attention worldwide. Huge efforts are dedicated to optimize indium nitride growth. However, this growth is extremely challenging, in particular using the metal organic vapor phase epitaxy (MOVPE) technique which exhibits very low growth rates. This may explain why most of the samples available in the scientific community, which also present the best electrical properties, were grown by molecular beam epitaxy (MBE). However, up to date, no intrinsic indium nitride layer was obtained. InN epilayer crystalline quality suffers from the lack of lattice matched substrates, leading to the use of double-step growth process. In this paper, we show that InN low lateral growth rate is a limiting parameter for efficient double-step growth process. But, we also report that the use of CBrCl3 during InN growth enhances the lateral growth rate. To improve the growth rate along the c-axis, we investigate alternative precursors for both nitrogen and indium species. We show that ammonia remains the best precursor, but combined with triethylindium, the growth rate increases with optimum crystalline quality. Finally, we compare MOVPE-grown and MBE-grown InN layers in order to understand the difference observed on the electrical properties. We show how thermal annealing can improve the MOVPE-grown InN layers leading to similar electrical properties than reported in MBE-grown samples. The role of ammonia as source of hydrogen is also discussed. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim