Two-Dimensional Growth of AlN and GaN on Lattice-Relaxed Al0.4Ga0.6N Buffer Layers Prepared with High-Temperature-Grown AlN Buffer on Sapphire Substrates and Fabrication of Multiple-Quantum-Well Structures

Lattice mismatch effects on AlN and GaN growth were studied, aiming at the realization of multiple-quantum-well (MQW) structures. Lattice-relaxed AlN, GaN and Al0.4Ga0.6N were prepared as buffer layers. Microcrystal islands were observed for AlN and GaN respectively grown on the GaN and AlN buffer layers, due to lattice mismatch. However, two-dimensional growth was observed for both layers on the Al0.4Ga0.6N buffer layer. This growth-mode change was ascribable to the fact that a lateral lattice constant for the Al0.4Ga0.6N surface, with residual in-plane compression, is almost the center between those of AlN and GaN. For the MQW structures grown on Al0.4Ga0.6N, it was thought that the AlN and GaN grew two-dimensionally and coherently without significant dislocation generation.