Microstructure and interface control of GaN/MgAl2O4 grown by metalorganic chemical vapor deposition: Substrate-orientation dependence.

GaN films with single-crystal and polycrystalline structure were deposited on (111) and (100) MgAl2O4 substrates by metalorganic chemical vapor deposition using a substrate modified by chemical etching and thermal passivation. The interface structure and chemical bonding state of the GaN/MgAl2O4 interface was investigated using angle-resolved x-ray photoelectron spectroscopy and resulting valence band spectra. Our results indicate that the Al2O3 buffered layer induced by thermal passivation of the (111) substrate remains unchanged during GaN deposition, which is primarily responsible for the epitaxial growth of GaN on (111) MgAl2O4 substrate. However, for the as-processed (100) substrate, interfacial reactions take place between the formed MgO-terminated surface and GaN films and GaN with a polycrystalline structure on (100) substrate forms. From the interface engineering viewpoint, the appropriate interface modification will allow control of the interface reaction to obtain high-quality GaN films for future optoelectronic devices. [ABSTRACT FROM AUTHOR]