Anisotropic strain relaxation in a-plane GaN quantum dots

Medium energy ion scattering (MEIS) has been used to measure at the monolayer scale the strain profile of self-organized GaN quantum dots grown on (11–20) or a-plane AlN by molecular-beam epitaxy. By confronting the MEIS results with a structural analysis carried out by atomic force microscopy, it is established that the strain profile is anisotropic, i.e., fully elastic along [1–100] and a combination of plastic and elastic along [0001]. High resolution transmission electron microscopy measurements reveal the presence of misfit dislocations with 1/2 [0001] Burgers vector, consistent with MEIS data