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In this study, Raman scattering measurements are reported on the BxGa1–xN layers grown on AlN-on-sapphire templates by MOVPE. The boron content covered the composition range from 0% (pure GaN) to 1.75%. The Raman spectra were recorded at 300 K with a confocal micro-Raman spectrometer in the backscattering geometries. Raman cartography at a lateral resolution of 1 µm was performed to study the spatial variation of the phonon peaks characteristics. The homogeneity of BGaN layers was studied and the phonon modes characteristics are determined as a function of composition, with respect to the laser polarisation. The E2 and A1(LO) modes frequencies are shifted with respect to the pure GaN. The A1(LO) mode behaviour correlates well with the free carriers concentration measured by Hall Effect method, indicating a phonon-plasmon coupling decreasing with increasing boron content in alloy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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)

In this report, the electrical and structural properties of BGaN thin films, with boron composition up to 2%, have been investigated. The resistivity, Hall mobility and carrier concentration were measured by the van der Pauw/Hall Effect technique, using annealed indium ohmic contacts. The current-voltage measurements between two planar gold and titanium/aluminum electrodes were performed. To analyze the structural properties, the polarized Raman spectra were measured with a micro-Raman spectrometer. The resistivity displays a strong increase with respect to the boron composition in BGaN alloy, directly related to the decrease of the n-type carrier concentration, while the mobility increases with boron content, well correlated to the structural measurements showing a good crystalline quality of the BGaN layers. This boron-controlled resistivity is very promising for using the BGaN based materials in microelectronic and optoelectronic devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)