Periodic oxide breakdown during oxidation of AlN/Sapphire(0001) films

We present an in situ synchrotron x-ray scattering study on the thermal oxidation of epitaxial AlN/Sapphire(0001) films. During annealing to 700degreesC, an epitaxial AlN film transforms progressively into a planar epitaxial gamma-Al2O3 layer. The oxidation proceeds through the gamma-Al2O3/AlN interfacial motion that is observed directly from the intensity fringes near the AlN(0002) Bragg reflection. The oxidation rate, deduced from the interfacial motion, exhibits repeating transitions from a linear to a parabolic oxidation behavior. This suggests that the oxide break down periodically. During the oxidation the strain in the remaining AlN reverts to the value measured at the same thickness during the growth of the AlN film. (C) 2002 American Institute of Physics.