The strain state of 1 and 2.5nm-thick GaN insertions into GaN/AlN nanocolumn heterostructures was studied by combining high-resolution transmission electron microscopy, Raman spectroscopy and theoretical modelling. It was found that the 2.5nm-thick GaN insertions were partially relaxed. This was attributed to the presence of dislocations in the external AlN capping layer; in close relationship with the morphology of GaN insertions and the AlN capping mechanism. The observed plastic relaxation in AlN was consistent with the small critical thickness expected for GaN/AlN radial heterostructures.

The Structural Properties of GaN Insertions in GaN/AlN Nanocolumn Heterostructures. C.Bougerol, R.Songmuang, D.Camacho, Y.M.Niquet, R.Mata, A.Cros, B.Daudin: Nanotechnology, 2009, 20[29], 295706