Microstructure of AlN with two-domain structure on (001) diamond substrate grown by metal-organic vapor phase epitaxy

We investigate the microstructures of domain boundaries in an AlN layer grown on a (001) diamond substrate by metal-organic vapor phase epitaxy. The AlN layer has a two-domain structure with crystal orientation along either <112?0> AlN named by AlN^I domain] or <101?0> AlN named by AlN^II domain] parallel to 110] direction of diamond. The AlN^I and AlN^II domains are not atomically bonded at two-domain boundary from initial to final step of growth, while an edge-type dislocation is generated at single-domain boundary (SDB). In addition, an inversion AlN^I domain named by AlN^I?] is randomly-ordered at the initial stage of the coalescence between the AlN^I domains. The AlN^I? is easily terminated with increasing the thickness of AlN^I domain. The inversion domain boundary changes to the edge-type dislocation at the SDB with further growth, which reduces the defect density in the AlN^I domains.