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AlInN epitaxial films with film thicknesses up to approximately 300 nm were grown nearly lattice-matched to a c-plane GaN-on-sapphire template by metalorganic chemical vapor deposition. The AlInN films showed relative good crystal qualities and flat surfaces, despite the existence of surface pits connected to dislocations in the underlying GaN film. The refractive index derived in this study agreed well with a previously reported result obtained over the whole visible wavelength region. The extinction coefficient spectrum exhibited a clear absorption edge, and the bandgap energy for AlInN nearly lattice-matched to GaN was determined to be approximately 4.0 eV.

Single-layer AlInN films with a film thickness of approximately 300 nm were grown on a c-plane free-standing (FS) GaN substrate by metalorganic chemical vapor deposition. The result showed that a highly flat-surface AlInN film with a small root-mean-square surface roughness of less than 0.5 nm was realized by adjusting its alloy composition to an almost perfectly lattice-matched to FS-GaN. As for the highly flat-surface AlInN film, the optical constants were evaluated in whole visible wavelength by spectroscopic ellipsometry. Then, its energy bandgap energy was determined to be 3.92 eV.

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Metalorganic chemical vapor deposition of approximately 300-nm thick epitaxial AlInN films with different alloy compositions was performed using a semi-relaxed c-plane GaInN template as an underlying substrate. The GaInN template consisted of a Ga0.98In0.02N film on a facet-structured GaN film formed on a c-plane sapphire substrate by the epitaxial lateral overgrowth technique, and its surface was treated with the chemical-mechanical polishing. It was observed that an Al0.835In0.165N film grown with an in-plane tensile strain exhibited a relatively smooth surface whereas an Al0.781In0.219N film grown with an in-plane compressive strain exhibited a granular morphology owing to a columnar polycrystalline structure. This phenomenon was quite similar to that observed for AlInN films grown non GaN/sapphire templates (GaN templates); therefore, it was speculated that the microstructure variation might have been caused by the in-plane compressive strain generated in AlInN films on the GaInN template in the same way as on GaN templates or FS-GaN substrates.