Metalorganic Vapor Phase Epitaxy Growth and Study of Stress in AlGaN Using Epitaxial AlN as Underlying Layer

The crystalline quality of AlGaN with high AlN molar fraction grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) was improved by using high-quality epitaxial AlN film on sapphire (0001). Atomically flat Al x Ga 1- x N (0.2< x <0.8) without any cracks was fabricated on the epitaxial AlN film. Lattice constants of the Al 0.48 Ga 0.52 N and the AlN at growth temperature were estimated from high-temperature X-ray diffraction measurement. The results showed that the in-plane lattice constant of the Al 0.48 Ga 0.52 N was stress-free or slightly compressed even at the growth temperature. The smaller in-plane lattice constant of AlN than that of AlGaN is considered to play a great important role in restraining generation of cracks.