Abstract

The fabrication of epitaxially grown crystalline dielectric oxide films is of great technological interest as these materials may be used as active waveguide devices and compact microlasers [1] as well as crystalline coatings in a thin- disc laser setup. For all these applications high-quality thin films are required, which are mainly determined by the interface between the substrate and the grown film. Rare-earth doped garnets have been widely used in solid-state lasers. Thus, we will report on lattice-matched film growth of these materials by the pulsed laser deposition technique. As Eu³+ is a highly sensitive spectroscopic probe ion for the investigation of the crystalline structure of the host material, it will be used. Starting with Eu-doped Y₃Al₅O₁₂ (YAG) films grown on sapphire and resulting in a lattice mismatch of a few percent, the structural and spectroscopic changes by gradually reducing the mismatch between the substrate and the film are investigated to a degree, where the film fits perfectly on the substrate (see fig. 1). Finally, the growth of the theoretically calculated, perfect lattice-matched system Eu:(Gd/Lu)AG on YAG is achieved. Within this contribution we will present the spectroscopic characterization of the systems a-Al₂O₃-Eu:Y₃Al₅O₁₂ resulting in a mismatch of a few percent, Y₃Al₅O₁₂-Eu:Y₃Al₅O₁₂ being lattice-matched except for the Eu-ions, and Y₃Al₅O₁₂- Eu:(Gd/Lu)₃Al₅O₁₂ with the mixing of Gd- and Lu-ions biasing the lattice disturbance of the Eu-doping. In order to obtain additional information, structural characterization by means of X-ray diffraction and atomic force microscopy has been performed. Also, the positive effect of post-PLD tempering the films at 1200°C has been investigated (see fig. 2). Even though the XRD spectra for as-grown PLD films indicate nearly perfect crystalline film growth, the corresponding emission spectra (grey shaded spectra in fig. 2) show a strong inhomogeneous broadening as it can be observed in amorphous films. In order to study these effects of the beginning film formation in more detail, upcoming experiments involve surface X-ray diffraction and atomic force microscopy. First improvements have been achieved by using a substrate temperature of 1000°C instead of 700°C during the ablation process.

© 2007 IEEE