In-situ deposited SiNx nanomask for crystal quality improvement in AlGaN

We report the growth of high crystal quality Al0.3Ga0.7N directly on sapphire substrates with metalorganic vapour phase epitaxy. We studied the improvements in crystal quality by introducing an in-situ deposited SiNx interlayer. It acts as a nanomask which results in termination of the dislocations near the interface between the nanomask and epilayer. The epilayers with no SiNx interlayer have very low density of screw type dislocations evident from transmission electron microscopy (TEM) investigations confirmed by a very narrow X-ray diffraction symmetric reflection (60”). This is a result of our oxygen doped AlN nucleation layer used to grow such epilayers. On the other hand, such epilayers have very broad XRD asymmetric reflections (typically a few thousand arcsec) indicating a high density of edge type dislocations. We could decrease the latter which are the main existing dislocations in our AlGaN epilayers. In TEM micrographs, we observed the formation of dislocation “bundles” when introducing SiNx interlayers. This phenomenon promotes the dislocation free areas on the surface of the wafer. We carried out accurate optimizations of the SiNx deposition. Consequently, we could grow high quality Al0.3Ga0.7N epilayers with much narrower XRD asymmetric peaks— 782” with total sample thickness of 1.4 μm.