Epitaxial orientation of III-nitrides grown on R-plane sapphire by metal-organic-vapor-phase epitaxy

The absolute epitaxial relationships between III-nitride films and R-plane sapphire are investigated using convergent beam electron diffraction. The resulting relationships are found to be[1−100]III-N‖‖[11−20]sapphire and [0001]III-N‖‖[−1101]sapphire, respectively. The O–Al bonds in the sapphire surface are antiparallel to the N-III bonds in the III-N films. High-resolution transmission electron microscopy shows that the AlN nucleation layer is asymmetrically strained. Along its c direction, the AlN layer is in extension whereas it is relaxed perpendicular to c;.This work is supported by the EU RTN Marie-Curie contract MRTN-CT2004-005583 (PARSEM). The authors want to thank I. Sellers for a critical reading of this letter.