The growth and structural properties of GaN/AlN core–shell nanowire heterostructures were studied using a combination of resonant X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy experiments. For a GaN core of 20nm diameter on average surrounded by an homogeneous AlN shell, the built-in strain in GaN was found to agree with theoretical calculations performed using a valence force field model. It was then concluded that for an AlN thickness up to at least 12nm both core and shell were in elastic equilibrium. However, in the case of an inhomogeneous growth of the AlN shell caused by the presence of steps on the sides of the GaN core, plastic relaxation was found to occur. Consistent with the presence of dislocations at the GaN/AlN interface, it was proposed that this plastic relaxation, especially efficient for AlN shell thickness above 3nm, was promoted by the shear strain induced by the AlN inhomogeneity.

The Structural Properties of GaN/AlN Core–Shell Nanocolumn Heterostructures. K.Hestroffer, R.Mata, D.Camacho, C.Leclere, G.Tourbot, Y.M.Niquet, A.Cros, C.Bougerol, H.Renevier, B.Daudin: Nanotechnology, 2010, 21[41], 415702