Résumé
We presented an experimental work on InN nanostructures grown on a GaN buffer layer deposited on sapphire (0001) by Metal Organic Vapor Phase Epitaxy. InN islands of controlled sizes were fabricated by using specific growth conditions and taking advantage of self-organization that results from Stranski-Krastanov growth mode. Then nanometric islands as small as 25 nm were characterized by using atomic force microscopy (AFM) and micro-Raman spectroscopy. AFM measurements revealed that the current shape of islands correspond to truncated hexagons. In-plane residual strain field was deduced from the E2 phonon frequency shift in micro-Raman spectra recorded on islands of various sizes. Careful analysis of these data made clear that the key parameter in determining the strain magnitude was the height of the islands: this was not surprising, keeping in mind that the shape was roughly independent of the size. Nevertheless, the dislocation density was believed to increase as function of the island thickness, leading to various degrees of strained relaxation, as probed by the present micro-Raman study. This conclusion was reinforced by the strain variation on the facets of single islands with respect to its value at the centre.