DOPING EFFECTS ON THE KINETICS OF SOLID-PHASE EPITAXIAL-GROWTH OF AMORPHOUS ALUMINA THIN-FILMS ON SAPPHIRE

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 substra tes by electron-beam evaporation. Iron or chromium atoms were uniforml y doped into the films during deposition to cation concentrations belo w 5 cationic %. The kinetics of the epitaxial growth were studied at 8 00-1050 degrees C in flowing oxygen gas by in situ time-resolved refle ctivity techniques as well as by ion backscattering and channeling tec hniques. A phase transformation sequence from amorphous through gamma to alpha alumina has been observed in all the undoped and doped films. The transformation from gamma to alpha alumina is a thermally activat ed process with an activation energy of 5.0+/-0.2 eV, independent of t he presence of dopants. However, the presence of dopants affects the o verall transformation rate. Fe enhances while Cr slows the growth rate relative to the undoped case. (C) 1995 American Institute of Physics.