An approach to using AlN/AlGaN superlattices for threading-dislocation density reduction when growing high-quality thick AlGaN layers on sapphire was described. By using X-ray diffraction measurements and etch-pit counting via atomic force microscopy, it was shown that the insertion of AlN/AlGaN superlattices suppressed mosaicity, decreased the threading dislocation density by 2 orders of magnitude and eliminated cracking. The dislocation densities which were deduced from the X-ray diffraction results, and those which were deduced from chemical etching, were found to be in good agreement.

AlN/AlGaN Superlattices as Dislocation Filter for Low-Threading-Dislocation Thick AlGaN Layers on Sapphire. H.M.Wang, J.P.Zhang, C.Q.Chen, Q.Fareed, J.W.Yang, M.A.Khan: Applied Physics Letters, 2002, 81[4], 604-6