FORMATION OF IRON OR CHROMIUM-DOPED EPITAXIAL SAPPHIRE THIN-FILMS ON SAPPHIRE SUBSTRATES

This work summarizes results of a simple procedure to incorporate dopa nts into the near surface region of single-crystal sapphire. We demons trate the formation of iron-doped and chromium-doped sapphire thin fil ms by solid-phase epitaxial growth. Amorphous alumina films of about 2 00-350 nm thickness were deposited onto single-crystal sapphire substr ates. Fe or Cr ions were introduced into the films during deposition. A post-deposition thermal process was performed in oxidizing ambients at 800-1400 degrees C to induce epitaxial growth and to incorporate do pants. The epitaxial relationship of the grown him with the substrate was confirmed by both ion channeling and cross-sectional transmission electron microscopy. The growth kinetics were determined by time-resol ved reflectivity measurements for different dopant concentrations. Ion channeling angular scans revealed that the Fe or Cr ions are incorpor ated onto octahedral sites (Al3+ sites) in the corundum structure as e xpected in equilibrium. External optical transmittance measurements ex hibited absorption in the near ultraviolet range associated with the F e3+ state. The substitution of Cr for Al3+ was also confirmed by the o bservation of R1 and R2 luminescence lines characteristic of ruby, The doping procedure has potential applications in the fabrication of thi n film planar optical waveguides and thin film stress sensors. (C) 199 5 American Institute of Physics.