Spatially, spectrally, and temporally resolved cathodoluminescence ͑CL͒ techniques have been employed to examine the optical properties and kinetics of carrier relaxation for metalorganic chemical vapor deposition grown InGaN/GaN single quantum wells ͑QWs͒. Cathodoluminescence wavelength imaging of the QW sample revealed local band gap variations, indicating the presence of local In composition fluctuations and segregation during growth. A detailed time-resolved CL study shows that carriers generated in the boundary regions will diffuse toward and recombine at InN-rich centers, resulting in a strong lateral excitonic localization prior to radiative recombination.

We have demonstrated that GaN can be grown epitaxially by atmospheric pressure metalorganic chemical vapor deposition on an aluminum oxide compound layer utilized as an intermediate layer between GaN and a Si͑111͒. X-ray diffraction measurement indicates that single-crystal hexagonal GaN with its basal plane parallel to the Si͑111͒ plane is grown. Using a scanning electron microscope, the macroscopic evolution of GaN grown on the AlO x /Si͑111͒ substrate is found to be similar to that of GaN grown on a sapphire͑0001͒ substrate. Cathodoluminescence ͑CL͒ spectrum shows a unique emission that consists of several peaks with the intensity comparable to that of the near-band-edge emission. Unique characteristics in CL spectrum are discussed in terms of a possible oxygen contamination of GaN grown on the AlO x /Si͑111͒ substrate.

An approach by which single crystal α-GaN can be grown laterally over oxidized AlAs (AlOx) formed on Si substrates is demonstrated. Regular α-Ga2-O3 stripe templates, spatially separated by AlOx, on which subsequent GaN growth is selectively seeded are formed. Since the boundary between the stripe template and AlOx is nominally planar, two pyramidal planes on separated GaN can merge by growing laterally over the AlOx (referred to as planar epitaxial lateral overgrowth). Transmission electron microscopy reveals that the number of structural defects in GaN laterally grown over the AlOx is remarkably reduced compared to that in GaN grown on the stripe templates, and accordingly cathodoluminescence reveals a strong band edge emission from GaN laterally grown over the AlOx, suggesting that this approach allows us to grow GaN on Si substrates with fewer defects.

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