Sandwich method to grow high quality AlN by MOCVD

We report pulsed atomic layer epitaxy growth of a very high crystalline quality, thick (similar to 2 mu m) and crack-free AlN material on c-plane sapphire substrates via a sandwich method using metal organic chemical vapor deposition. This sandwich method involves the introduction of a relatively low temperature (1050 degrees C) 1500 nm thick AlN layer between two 250 nm thick AlN layers which are grown at higher temperature (1170 degrees C). The surface morphology and crystalline quality remarkably improve using this sandwich method. A 2 mu m thick AlN layer was realized with 33 arcsec and 136 arcsec full width at half maximum values for symmetric (0002) and asymmetric (10 (1) over bar5) reflections of omega-scan, respectively, and it has an atomic force microscopy root-mean-square surface roughness of similar to 0.71 nm for a 5 x 5 mu m(2) surface area.