Characterization of a-plane InN film grown on r-plane sapphire by MOCVD

A-plane InN film has been grown on r-plane sapphire substrate by MOCVD without any buffer. X-ray ω/2θ scan confirms that only wurtzite-type InN was grown. The in-plane orientation relationship between a-plane InN and r-plane sapphire is 〈0 0 0 1〉InN//[1¯ 1 0 1]sapphire and [1¯ 1 0 0]InN//[1 1 2¯ 0]sapphire deduced from selected area diffraction. Atomic force microscopy reveals that no stripe features appear on surface of the a-plane InN film, which is different from that of a-plane GaN grown on r-plane sapphire where stripes along [0 0 0 1] direction appear on the surface. The difference originates from the different growth mode of InN and GaN. In addition, photoluminescence and absorption spectra show that our a-plane InN has a narrow band gap of 0.7 eV, which is similar to that of c-plane InN film grown by the same system.