Characterization of rf-sputtered InN films and AlN/InN bilayers on (0001) sapphire by the x-ray precession method

Thin films of InN and AlN/InN bilayers have been deposited on (0001) sapphire at a variety of substrate temperatures by reactive rf-magnetron sputtering. For all films, the c axis of the metal nitride film parallels the c axis of the sapphire substrate, and the transmission x-ray precession method has been employed to study the nature and azimuthal coherence of the in-plane heteroepitaxy. For the InN films, a mixture of textured and epitaxial grains persists up to ∼200 °C and solely epitaxial grains are observed at higher substrate temperatures, to a maximum adherence temperature of 525 °C. In contrast, the AlN/InN bilayers are epitaxial at substrate temperatures of 50 °C and above, and a uniform deposition can be retained up to 650 °C. These fundamental differences in adhesion, structure and morphology of the InN films and the AlN/InN bilayers on (0001) sapphire are also clearly reflected, for example, in the variation in electrical mobility with substrate deposition temperature.