AlN/AlGaN superlattices as dislocation filter for low-threading-dislocation thick AlGaN layers on sapphire

We report on an approach of using AlN/AlGaN superlattices (SLs) for threading-dislocation-density reduction to grow high quality thick AlGaN on sapphire. Using x-ray diffraction (XRD) measurements and etch pits counting by atomic force microscopy, we show that the insertion of AlN/AlGaN SLs suppresses the material mosaicity and decreases the threading dislocation density by two orders of magnitude, and then eliminates cracking. Dislocation densities deduced from the XRD results and those from chemical etching are in a good agreement.