Synthesis of epitaxial γ-Al2O3 thin films by thermal oxidation of AlN/sapphire(0001) thin films

The synthesis of epitaxial gamma-Al2O3 films by oxidizing AlN/sapphire(0001) films was investigated in a synchrotron X-ray scattering experiment. Porous gamma-Al2O3 nucleates on the surface of the AlN film when annealed above 700degreesC in oxygen ambient. As the annealing temperature increases above 900degreesC, the entire AlN film is oxidized into an epitaxial gamma-Al2O3 film that has a cubic spinel structure. With increasing oxidation temperature, more oxygen atoms are incorporated into the oxide structure, resulting in denser oxide films with a larger lattice constant. The crystal domain size increases from 50 Angstrom to 210 Angstrom, suggesting that the initial nucleation of the gamma-Al2O3 crystalline domains is followed by gradual grain growth.