Channeling Investigation of the Lattice Location of Ti in Ti-Implanted Optical Waveguides in LiNbO 3
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CHANNELING INVESTIGATION OF THE LATTICE LOCATION OF Ti IN Ti-IMPLANTED OPTICAL WAVEGUIDES IN LiNbO3
Ch. Buchal and S. Mantl IFF/KFA, D-5170 Jilich, W. Germany, and D.K. Thomas Solid State Div., ORNL, Oak Ridge TN 37831
ABSTRACT Ion channeling of 3 MeV He ions has been employed to investigate the lattice location of Ti in Ti implanted optical waveguides in LiNbO3 after Solid Phase Epitaxy. Particle-Induced X-rays (PIXE) from Ti at 4.5 keY (Ko ) and Nb at 2.2 keV (Lq) and 16.6 keV (Koe) have been detected and analyzed simultaneously. All scans yield similar behaviour of the Ti and the Nb signals. This provides clear evidence, that within well annealed implanted waveguides the Ti4+ and the Nb5 + ions occupy equivalent lattice positions. INTRODUCTION Crystals of LiNbO 3 play an important role in the fabrication of integrated optical devices, since high quality single crystals are commercially available, and the material is strong, stable and easily polished (1] . LiNbO3 has a good electrooptical coefficient, which permits the use of low control voltages. It also has very low optical transmission losses and may be used for a broad range of useful wavelengths [2,3]. There exists a well established technology of fabricating optical waveguiding devices by diffusing Titanium into the LiNbO3 substrate at temperatures around 1000"C [4] The local ordinary and extraordinary indices are increased proportional to the Ti concentration [5,6] , and especially for long wavelength applications high Ti concentrations are most desirable. This objective led to the introduction of ion implantation for Ti doping and very successful devices have Work at Oak Ridge sponsored by the Div. Mat. Sciences, USDOE, under contract DE-AC05-840R21400 with Martin Marietta Energy Syst. Mat. Res. Soc. Symp. Proc. Vol. 100. 11988 Materials Research Society
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been fabricated by implanting Ti and employing a rapid epitaxial regrowth to remove the radiation damage [7,8]. These experiments have been extended to low dose implants in order to study the nature of the observed Solid Phase Epitaxy [9].
The observed threshold temperatures for the ionic i.e. 200 0 C for Lithium, 500°C for Oxygen, and
mobilities,
probably around 800°C for Ti may explain the different regrowth character at low doses, where only Lithium and Oxygen are mobile, and at high doses, where additional Ti diffusion is observed [7,9]. The successful use of diffusion techniques for LiNbO3 substrates is directly related to the "open" lattice structure of this material [10]. Amazingly one suspects the Ti to diffuse into LiNbO3 in the form of it's oxide TiO2 [1,11]. This is in contrast to the classical perovskites, which do not permit easy diffusion doping. Their lattice is more densely packed [12], and the electrooptical materials BaTiO 3 and KNbO 3 cannot be doped by diffusion. As ion implantation into LiNbO3 introduces a high amount of additional Ti, the corresponding strong change of the local stochiometry might lead to lattice instabilities or even
1600
T Nb
o 12800
Olgy-Si
400
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