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The structural properties of InGaN/GaN multiple quantum wells (MQW) were studied using synchrotron based high resolution x-ray diffraction (HRXRD). MQW structures were grown on the top and sidewall facets of triangular and trapezoidal shaped GaN ridges by metalorganic vapour phase epitaxy (MOVPE) in the regime of selective area growth (SAG). Period and strain variations as a function of oxide mask width were determined for both the sidewall and the top facet growth. Oxide mask widths ranged between 2 and 20 µm with openings between adjacent masks of 4 and 6 µm. Analysis of the x-ray diffraction curves revealed a sidewall / vertical growth rate ratio of ∼0.3 through a comparison of the top to sidewall facet MQW periods. Masks orientated along the 〈11-20〉 crystallographic direction showed stronger growth enhancement along with large global strain for MQW growth on the top (0001) plane. Interpreting our results within the framework of vapour phase diffusion revealed that inter-facet migration of group-III species needs to be taken into account. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Transmission spectroscopy has been used to investigate the in-plane linear birefringence of GaAs/AlAs multiple quantum wells (MQWs) with symmetric wells/barriers from 20/20 to 70/70 A. Varying optical thicknesses of the samples have been used to measure a reference value of the birefringence. While the resonant part in the dispersion of the birefringence has been attributed to the contribution from the confined electronic gaps, a nonresonant background birefringence has been analyzed as a function of the MQW period and explained by the presence of local fields.

International audience; We report epitaxial growth of GaN layers on z- and x-cut LiNbO3 substrates using MOVPE. GaN layers with the thick- ness of 450 nm were characterized using X-ray diffraction. For both, z- and x-cut orientations of LiNbO3 substrates, the GaN layers have c-axis orientation normal to the substrate plane and the in-plane lattice orientation of GaN layers coin- cides with the primary axes of LiNbO3 substrates. Although GaN layers exhibit almost complete strain relaxation, the re- sidual compressive strain determined with respect to a free- standing GaN is of the order of +0.37% and +0.2% for z- and x-cut substrates, respectively.

GaN nanodots and nanostripes with smooth sidewall surfaces have been selectively grown on 6H-SiC substrates by metal organic vapor phase epitaxy. By varying the growth reactor pressure, we have been able to grow either isolated nanostructures or laterally overgrown structures. As confirmed by the Raman scattering and X-ray diffraction techniques, the nanostructures have no influence of step bunching that occurs in the unmasked area of the continuous GaN film. The frequency shift of the E2 optical phonons shows that the residual strain in the nanostripes is relaxed compared to the continuous GaN film. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)