Eu-doped Yttria and Lutetia Thin Films Grown on Sapphire by PLD
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Eu-doped Yttria and Lutetia Thin Films Grown on Sapphire by PLD S. Bär1, H. Scheife1, G. Huber1, J. Gonzalo2, A. Perea2, A.Climent Font3, F. Paszti3, M. Munz4 1 Institut für Laser-Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany 2 Instituto de Optica, CSIC, Serrano 121, 28006 Madrid, Spain 3 Departamento de Física Aplicada y ICMAM, Universidad Autonoma de Madrid, 28049 Cantoblanco, Madrid, Spain 4 Bundesanstalt für Materialforschung und –prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany ABSTRACT This paper focuses on the preparation and characterization of crystalline thin films of rare-earth-doped sesquioxides (Y2O3 and Lu2O3) grown by pulsed laser deposition on singlecrystal (0001) sapphire substrates. The crystal structure of the films (thicknesses between 1 nm and 500 nm) was determined by X-ray diffraction and surface X-ray diffraction analysis. These measurements show that the films were highly textured along the 〈111〉 direction. Using Rutherford backscattering analysis the correct stoichiometric composition of the films could be proved. The surface morphology of the thin films has been studied using atomic force microscopy. Crystalline films show a triangular surface morphology, which is attributed to the 〈111〉 growth direction. The emission and excitation spectra of the Eu-doped films down to a thickness of 100 nm look similar to those of the corresponding crystalline bulk material, whereas films with a thickness ≤ 20 nm show a completely different emission behaviour. INTRODUCTION The development of integrated optic devices demands the fabrication of high quality optically active thin films. This work focuses in particular on thin sesquioxide films, which are promising materials because they are well-known hosts for rare-earth-doped luminescent materials and solid-state lasers, e. g. Yb:Y2O3 [1]. Other potential applications are phosphor materials, high-temperature corrosion protection, and, due to the large band gap and a high dielectric constant, these materials can be used in semiconductor devices, e.g. MIS diodes, transistor gates, MOS capacitors, and DRAM [2,3,4]. Additionally, the fabrication of planar waveguide structures can be envisioned. These devices can be passive elements as well as active waveguides, where the larger emission and absorption cross sections available in crystalline matrices compared to fibres become accessible, and the confine-ment of light inside the waveguide generates a larger intensity-length product. Additionally, the guiding of the pump mode as well as the signal mode leads to an excellent overlap of the modes resulting in lower laser thresholds. For the selection of a substrate for the growth of thin films with optical quality several require-ments must be considered: good transmission in a wide range of wavelengths, a refractive index lower than that of the growing film, low cost, and a good thermal and lattice match with the chosen film. As all these conditions are widely fulfilled, sapphire is an attractive substrate can-didate
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