AlN Periodic Multiple-layer Structures Grown by MOVPE for High Quality Buffer Layer

High crystal quality crack-free AlN on sapphire was grown by low pressure metal organic vapor phase epitaxy (MOVPE). Growth experiments combine two recent approaches: the ammonia pulse-flow method and ammonia continuous-flow growth mode by varying the V/III ratio. The detailed aspects of MOVPE, employing the periodic multilayer approach at low, intermediate, and high temperatures are described. This method yields significant reduction of screw dislocation density and provides very smooth surface for thin AlN layers.