Doping effects on the kinetics of solid-phase epitaxial growth of amorphous alumina thin films on sapphire

Abstract

The effects of doping on the kinetics of solid-phase epitaxial growth of amorphous alumina have been studied. Amorphous alumina Al2O3) thin films, 200–265 mm thick, were deposited on to (0001) sapphire substrates by electron-beam evaporation. Iron or chromium atoms were uniformly doped into the films during deposition to cation concentrations below 5 cationic %. The kinetics of the epitaxial growth were studied at 800–1050 °C in flowing oxygen gas by in situ time-resolved reflectivity techniques as well as by ion backscattering and channeling techniques. A phase transformation sequence from amorphous through gamma to alpha alumina has been observed in all the undoped and doped films. The transformation from γ to α alumina is a thermally activated process with an activation energy of 5.0±0.2 eV, independent of the presence of dopants. However, the presence of dopants affects the overall transformation rate. Fe enhances while Cr slows the growth rate relative to the undoped case.