Growth of KTiOPO 4 Films on KTi 1-x Ge x OPO 4 Substrates by Liquid-phase Epitaxy
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Nikolov Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
A. Vilalta, J.J. Carvajal, J. Massons, Jna. Gavalda`, M. Aguilo´, and F. Dı´aza) Laboratori de Física Aplicada i Cristal.lografia and IEA, Universitat Rovira i Virgili, 43005 Tarragona, Spain (Received 23 January 2001; accepted 12 December 2001)
The epitaxial growth of KTiOPO4 (KTP) films on different natural faces of KTi1−xGexOPO4 substrates was studied. The growth on faces (100) and (201) is generally of high quality, irrespective of the growth time or concentration of germanium in the substrates. On the other hand, the epitaxial growth on the face (101) is always of poor quality, and the defects are pyramids, even when the germanium content in the substrate is low and the growth time is short. The films on faces (011) and (110) generally have small hillocks as defects and for high concentrations of Ge in the crystals some cracks begin to appear. The film thickness, depending on the growth time and the face considered was measured by scanning electron microscopy (SEM) using backscattered electrons. The diffusion of germanium from the substrate to the film is very low, as demonstrated by electron probe microanalysis measurements and SEM observations. The difference in the refractive indices ny and nz of KTP and KTi0.92Ge0.08OPO4 are on the order of 0.01, which could be enough to produce wave guides. Finally, it was observed that the second harmonic generation response of KTP substituted with Ge decreases as the Ge content in the crystal increases. I. INTRODUCTION
Due to its important nonlinear optical properties, high laser damage threshold, and chemical stability, potassium titanyl phosphate, KTiOPO4 (KTP), is one of the best materials for optical and electro-optical applications.1,2 It is also important in the fabrication of optical wave guides for optical switches and modulators.3–5 Because KTP melts incongruently,6 it cannot be grown by the usual melt techniques. Single crystals of KTP have been obtained by hydrothermal and flux growth methods.6,7 Good-quality single-crystal films of KTP suitable for producing optical wave guides can be obtained by liquid-phase epitaxy (LPE) on substrates of the same family. This can be done by controlling the mismatch between the cell parameters of the substrate and those of the film, using the solid solutions offered by this family of crystals. Unlike other techniques used to fabricate wave guides, such as ion exchange, the LPE technique permits one to obtain a homogeneous single crystal film and allows control of the film thickness by adjusting the supersaturation of the solution and the growth time.8,9 Thin films of RbxK1−xTiOPO4 on KTP substrates have already been grown by LPE.8 However, monovalent cations are characterized by their mobility in the KTP a)
Address all correspondence to this author. J. Mater. Res., Vol. 17, No. 3, Mar 2002
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lattice, and the diffusion of Rb ions into the substrate. There is a con
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