The structural properties of GaN/AlN core–shell nanocolumn heterostructures

Abstract

The growth and structural properties of GaN/AlN core–shell nanowire heterostructureshave been studied using a combination of resonant x-ray diffraction, Raman spectroscopyand high resolution transmission electron microscopy experiments. For a GaN core of 20 nmdiameter on average surrounded by a homogeneous AlN shell, the built-in strain in GaN isfound to agree with theoretical calculations performed using a valence force field model. Itis then concluded that for an AlN thickness up to at least 12 nm both core and shell are inelastic equilibrium. However, in the case of an inhomogeneous growth of the AlN shellcaused by the presence of steps on the sides of the GaN core, plastic relaxation is found tooccur. Consistent with the presence of dislocations at the GaN/AlN interface, it isproposed that this plastic relaxation, especially efficient for AlN shell thicknessabove 3 nm, is promoted by the shear strain induced by the AlN inhomogeneity.