We use Raman scattering to investigate the composition behavior of the E 2h and A 1 (LO) phonons of In x Ga 1Àx N and to evaluate the role of lateral compositional fluctuations and in-depth strain/ composition gradients on the frequency of the A 1 (LO) bands. For this purpose, we have performed visible and ultraviolet Raman measurements on a set of high-quality epilayers grown by molecular beam epitaxy with In contents over a wide composition range (0.25 < x < 0.75). While the as-measured A 1 (LO) frequency values strongly deviate from the linear dispersion predicted by the modified random-element isodisplacement (MREI) model, we show that the strain-corrected A 1 (LO) frequencies are qualitatively in good agreement with the expected linear dependence. In contrast, we find that the strain-corrected E 2h frequencies exhibit a bowing in relation to the linear behavior predicted by the MREI model. Such bowing should be taken into account to evaluate the composition or the strain state of InGaN material from the E 2h peak frequencies. We show that in-depth strain/composition gradients and selective resonance excitation effects have a strong impact on the frequency of the A 1 (LO) mode, making very difficult the use of this mode to evaluate the strain state or the composition of InGaN material. V C 2012 American Institute of Physics.

The growth of 3C-SiC on (001) silicon substrates by means of vapor phase epitaxy is described. The growth mechanisms are discussed with the aid of structural and morphological characterizations performed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. Raman spectroscopy was used to study the residual stress. A large shift of Raman peaks with respect to the expected values for the bulk is observed and explained by the relaxation of Raman selection rules due to lattice defects. The stress and stress gradients through the film thickness are observed and studied on micrometer-sized structures such as membranes and cantilevers. Local Raman peak fluctuations are observed on millimeter-sized membranes, while cantilevers show different degrees of curling depending on film thickness.

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Multicrystalline silicon (mc-Si) is increasingly used in the photovoltaic industry. However, this material is characterized by intrinsic structural heterogeneities (dislocations, grain boundaries, etc.), which are detrimental to the performance of the cells. The minority-carrier diffusion length is sensitive to these defects, and gives an indication of the material quality and its suitability for solar cell use. The laser beam induced current (LBIC) technique makes it possible to estimate the local minority-carrier diffusion length from photocurrent contrast data. The purpose of this work is to show an advanced homemade LBIC system that highlights the importance of controlling the laser power excitation and the reflected light in inhomogeneous mc-Si samples. This control demonstrates that the estimated minority-carrier diffusion length (L Diff ) in texturized multicrystalline wafers strongly depends on the collecting conditions of the reflected light.

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