Article | REF: E6308 V1

Crystalline thin films Elaboration processes and applications

Authors: Gurvan BRASSE, Patrice CAMY

Publication date: October 10, 2018

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ABSTRACT

Since the end of the 1970s, thin films have attracted growing interest in many fields especially for photonic applications, owing to increasing needs in telecoms, biophotonics, the environment, defense, and civil protection. This article describes the main methods for making optical dielectric crystalline thin films, and their related characterization techniques, and gives some examples of applications based on the results reported internationally to date.

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AUTHORS

  • Gurvan BRASSE: CNRS Research Engineer Centre de recherche sur les ions, les matériaux et la photonique (CIMAP) UMR 6252 CEA-CNRS-ENSICAEN, Université de Caen Normandie, Caen, France

  • Patrice CAMY: Professor at the University of Caen – Normandie Centre de recherche sur les ions, les matériaux et la photonique (CIMAP) UMR 6252 CEA-CNRS-ENSICAEN, University of Caen Normandie, Caen, France

 INTRODUCTION

The physical chemistry of thin films is driving innovation and research, and is playing an increasingly important role in materials science. Among the many fields in which thin films are of interest, optics and photonics have made a major contribution to their development, particularly since the late 1970s, with the development of semiconductor materials. Many devices have been developed using thin films, including lasers, scintillators, waveguides and optical amplifiers. The deposition of thin films has also contributed to the functionalization of surfaces, by conferring certain properties: antireflection, photochromism, electrochromism, photocatalysis, photoluminescence or electroluminescence... More recently, the emergence of integrated optics has opened up new prospects, such as the multiplication of active and passive optical functions on a single substrate by structuring materials in the form of thin films using "top down" or "bottom up" approaches.

These thin films can be amorphous, crystalline or ceramic, and can be semiconducting or dielectric. For the sake of brevity, this article deals only with dielectric crystalline thin films, with thicknesses ranging from a few microns to a few hundred microns, which offer new and complementary application prospects to those offered by massive crystals.

We begin with an overview of the dielectric thin films currently being developed for optical and optoelectronic applications, and present the state of the art of the main techniques used to produce them. We then turn our attention to the Liquid Phase Epitaxy (LPE) technique, one of the most suitable methods for producing high-quality, micrometer-thick crystalline thin films. After defining the concept of epitaxy and the principle of the LPE technique, we present the different mechanisms involved in epitaxial growth, and introduce a few thermodynamic and kinetic considerations to better understand the phenomena involved. We then take a more experimental approach to the physical chemistry involved in synthesizing crystalline thin films of various materials of optical interest, based on fluorides on the one hand, and oxides on the other. The difficulties inherent in growing these materials, the importance of the substrates and solvents used, and the influence of experimental parameters are then discussed. We also highlight the crucial importance of the cleaning, shaping and polishing stages of epitaxial thin films, before discussing various possibilities for "post-processing" such samples, to optimize some of their properties according to the applications targeted. A non-exhaustive list of the various characterization techniques that can be used to characterize these samples is then presented. Finally, we present several examples of applications and devices based on rare-earth...

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KEYWORDS

laser   |   crystalline thin films   |   liquid phase epitaxy   |   optic


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