Synthesis of epitaxial γAl2O3 thin films by thermal oxidation of AlN/sapphire(0001) thin films

The synthesis of epitaxial γAl2O3 films by oxidizing AlN/sapphire(0001) films was investigated in a synchrotron X-ray scattering experiment. Porous γAl2O3 nucleates on the surface of the AlN film when annealed above 700 °C in oxygen ambient. As the annealing temperature increases above 900 °C, the entire AlN film is oxidized into an epitaxial γAl2O3 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 Å to 210 Å, suggesting that the initial nucleation of the γAl2O3 crystalline domains is followed by gradual grain growth.