Growth mechanism of c-axis-oriented AlN on (1 1 1) diamond substrates by metal-organic vapor phase epitaxy

c-Axis-oriented wurtzite (0 0 0 1) AlN layers are grown on a (1 1 1) diamond substrate by metal-organic vapor phase epitaxy. The microstructure and growth mechanism of the AlN layer are examined using X-ray diffractometry and transmission electron microscopy. At the initial stage of AlN growth, AlN particles with a two-domain structure are nucleated on the (1 1 1) diamond surface. The orientation is either 〈1 1 2¯ 0〉AlN ∥ [1 1¯ 0] diamond [named the AlNI domain] or 〈1 0 1¯ 0〉AlN ∥ [1 1¯ 0] diamond with a rotation angle of 30° from AlNI around the c-axis [named the AlNII domain]. The initial AlN particles are predominantly composed of AlNII. Subsequently, the AlNII grains incorporate the quite-low-density AlNI grains upon further growth. Finally, a continuous AlN layer dominated by the AlNII domain is obtained on the diamond. The growth dynamics is significantly different from that of the AlN layer grown on (1 1 1) Si. The growth mechanism is understood by considering the periodic atomic arrangement of AlN and (1 1 1) diamond. We conclude that AlNII on (1 1 1) diamond has a geometrically appropriate epitaxial relationship that reduces the stress energy of the AlN lattice.