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InGaN alloys are of raising interest for many applications. The possibility of tuning their functional properties with the composition sets the importance of finding methods to characterize these materials in a fast and non-destructive way. Raman spectroscopy is one of these techniques, being able to yield information about the composition, strain, and other relevant parameters. However, the method of measuring the composition with a calibration of the maximum A1(LO) band is today limited to regions which are either rich in In or in Ga. The middle composition range still needs a calibration. By measuring the Raman spectra of different InxGa1-xN alloys grown epitaxially on Si and by comparing them with the results from X-ray diffraction, we investigated this missing region of compositions. Within the range of 30%–65%, we have found that the position of the maximum of A1(LO) scales with the In fraction x as ωx = 736 – 135x – 24x2 cm−1. With this calibration, it is possible to determine, by Raman spectroscopy, the composition of an unknown alloy with an uncertainty of 5%. [ABSTRACT FROM AUTHOR]

A hybrid metal–semiconductor nanosystem for the generation of THz radiation, based on the fabrication of GaAs quantum molecules-Ga metal nanoparticles complexes through a self assembly approach, is proposed. The role of the growth parameters, the substrate temperature, the Ga and As flux during the quantum dot molecule (QDM) fabrication and the metal nanoparticle alignment are discussed. The tuning of the relative positioning of QDMs and metal nanoparticles is obtained through the careful control of Ga droplet nucleation sites via Ga surface diffusion. The electronic structure of a typical QDM was evaluated on the base of the morphological characterizations performed by atomic force microscopy and cross sectional scanning electron microscopy, and the predicted results confirmed by micro-photoluminescence experiments, showing that the Ga metal nanoparticle-GaAs quantum molecule complexes are suitable for terahertz generation from intraband transition. [ABSTRACT FROM AUTHOR]

In As atmosphere, we analyzed the crystallization dynamics during post-growth annealing of Ga droplets residing at the top of self-assisted GaAs nanowires grown by molecular beam epitaxy. The final crystallization steps, fundamental to determining the top facet nanowire morphology, proceeded via a balance of Ga crystallization via vapor-liquid-solid and layer-by-layer growth around the droplet, promoted by Ga diffusion out of the droplet perimeter, As desorption, and diffusion dynamics. By controlling As flux and substrate temperature the transformation of Ga droplets into nanowire segments with a top surface flat and parallel to the substrate was achieved, thus opening the possibility to realize atomically sharp vertical heterostructures in III-As self-assisted nanowires through group III exchange. [ABSTRACT FROM AUTHOR]