Growth and Characteristics of Single Crystals of Lithium Niobate
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V6.11.1
Growth and Characteristics of Single Crystals of Lithium Niobate A. K. Batra, T. Gebre, J. Stephens, M. D. Aggarwal and R. B. Lal Department of Physics, P. O. Box 1268 Alabama A&M University, Normal, Alabama 35762 (USA) ABSTRACT Lithium niobate single crystal is an excellent material for various optical applications such as frequency conversion, optical switches, optical modulators and others. An automatic diameter control Czochralski crystals growth system has been designed and fabricated. A brief description of the entire system along with software developed has been described. With optimized growth parameters, pure and Fe/Mn doped crystals have been successfully grown using this system. Preliminary characterizations of these crystals have also been presented. INTRODUCTION Ferroelectric Lithium Niobate (LiNbO3 or LN) possesses a combination of unique electro optical, nonlinear optical, acoustic, piezoelectric, pyroelectric and photorefractive properties making it a suitable for applications in various optical devices, air force acceleration meters, filters in television receivers and holographic recording medium etc. [1-3]. An indispensable condition for some of these applications is a high degree of optical uniformity of LN crystals with stoichiometric composition in terms of the [Li]/[Nb] ratio. However, it is well known that many physical characteristics of LN depend strongly on the presence of defects and dopants present in the crystal lattice. The intrinsic ions defects related to the non-stoichiometry greatly affects the electro-optic and nonlinear optical properties [4-5]. Some of the dopants and intrinsic defects can enhance the optical damage threshold [6-7] and photorefractive properties (8-9). The introduction of dopants from the first transition series, iron (Fe) and manganese (Mn) have been carried out to improve the photorefractive properties of the crystal. It is therefore of importance to control the real composition of the crystal or its deviation from the stoichiometric composition or crystals growth with suitable dopants. In this paper, we describe a Czochralski Crystal Growth System which has unique features to permit automatic adjustment of the power level to the furnace in order to maintain a specific diameter during the growth process along with software developed in Visual Basic 6.0. Using this automatic diameter control system, Fe-doped lithium niobate crystal (LN:Fe) and co-doped with Mn (LN:Fe/Mn) have been reproducibly grown. The results of the crystal growth parameters with respect to temperature, diameter and time are presented along with compositional characterization using Rutherford backscattering spectrometry based on the detection of elastic light ions which are scattered by a crystalline target. The preliminary results of investigation of I-V and conductivity of pure and doped crystals are also presented.
V6.11.2
EXPERIMENTAL Crystal growth System: To reproducibly grow high-quality single crystals, the automatic diameter control system for Czochralski crystal growth
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