Microstructure variation in thick AlInN films grown on c-plane GaN on sapphire by metalorganic chemical vapor deposition

300-nm-thick AlInN films with InN molar fractions ranging from 0.114 to 0.197 were grown by metalorganic chemical vapor deposition on c-plane GaN on sapphire. It was confirmed that no lattice relaxation occurred for samples with InN molar fractions from 0.144 to 0.197, and the InAlN films with low InN molar fractions showed a relative smooth surface. However, it turned into a granular surface morphology resulting from a columnar polycrystalline structure when the InN molar fraction exceeded a compositional boundary of in-plane lattice matching. As for the smooth-surface AlInN single-layers, the optical constants as well as energy bandgaps were determined.