Influence of the microstructure on the optical characteristics of SrTiO 3 thin films
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Stafford Université de Montréal, Département de Physique, Montréal, Québec H3C 3J7, Canada
A. Amassian École Polytechnique de Montréal, Département de Génie Physique, Montréal, Québec H3C 3A7, Canada
M. Chaker Institut National de la Recherche Scientifique Énergie, Matériaux et Télécommunications, Varennes, Québec J3X 1S2, Canada
J. Margot Université de Montréal, Département de Physique, Montréal, Québec H3C 3J7, Canada
L. Martinu École Polytechnique de Montréal, Département de Génie Physique, Montréal, Québec H3C 3A7, Canada
M. Kulishov Adtek Photomask Inc, Montre´al, Québec H4T 1J6, Canada (Received 4 August 2004; accepted 17 September 2004)
The influence of the microstructure of strontium-titanate-oxide (SrTiO3 or STO) thin films on their optical properties was investigated through an extensive characterization. The STO films have been deposited on silicon substrates by reactive pulsed laser deposition. The effect of the oxygen deposition pressure on the crystalline quality of the films was systematically studied by x-ray diffraction and scanning electron microscopy. Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and secondary ion mass spectrometry were used to determine the atomic density and depth concentration profiles of the various species forming the film. The refractive index and extinction coefficient were obtained using variable angle spectroscopic ellipsometry. Based on this full characterization, it is demonstrated that the optical characteristics of the films are directly correlated to their microstructural properties. In particular, the refractive index increases with film density, while losses decrease. In addition, the interface between STO and Si is characterized by an interdiffusion layer. As the deposition pressure is enhanced, the width of this layer significantly increases, inducing localized inhomogeneity of the refractive index. I. INTRODUCTION
Strontium-titanate-oxide (SrTiO3 or STO) is of great interest for several applications, including very large scale integrated circuits required for dynamic random access memories, antireflective coatings in optoelectronic devices and oxygen sensors.1–3 STO has also been used as a suitable substrate for depositing thin films of various oxides such as high temperature superconducting materials.3–5 Fabrication of STO thin films for applications in electrical devices was also reported.6–11 Clearly,
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0002 68
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 1, Jan 2005 Downloaded: 14 Mar 2015
the integration of STO thin films into a device requires an excellent control of their physical properties. Several authors have examined the growth mechanisms as well as the microstructural, electrical, and optical properties of STO films.3,6–17 However, most of these works remain rather descriptive and do not report any correlation between the film properties and their electrical or optical characteristics. The present w
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