Optical Waveguide Formation by Ion Implantation of Ti or Ag
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OPTICAL WAVEGUIDE FORMATION BY ION IMPLANTATION OF Ti OR Ag t D. B. POKER AND D. K. THOMAS Oak Ridge National Laboratory, Oak Ridge, TN 37831-6057
ABSTRACT Ion implantation of Ti into LINbO3 has been shown to be an effective means of producing optical waveguides, while maintaining better control over the resulting concentration profile of the dopant than can be achieved by in-diffusion. While undoped, amorphous LiNbO3 can be regrown by solid-phase epitaxy at 4000C with a regrowth velocity of 250 A/min, the higher concentrations of Ti required to form a waveguide (-10%) slow the regrowth considerably, so that temperatures approaching 800'C are used. Complete removal of residual damage requires annealing temperatures of 1000°C, not significantly lower than those used with in-diffusion. Solid phase epitaxy of Agimplanted LiNbO 3 , however, occurs at much lower temperatures. The regrowth is completed at 400°C, and annealing of all residual damage occurs at or below 800°C. Furthermore, the regrowth rate is independent of Ag concentration up to the highest dose implanted to date, 1 x 1017 Ag/cm 2 . The usefulness of Ag implantation for the formation of optical waveguides is limited, however, by the higher mobility of Ag at the annealing temperature, compared to Ti. INTRODUCTION The use of ion implantation in the production of optical waveguides in LiNbO 3 has been shown to exhibit several advantages over thermal diffusion, namely: shallower guides, higher concentration of dopant, steeper gradients, and better control of dopant profiles.' However, the ion implantation process introduces damage to the substrate sufficient to drive it amorphous. The crystallinity and stoichiometry can be restored by solid-phase epitaxy (SPE) in a water-saturated oxygen atmosphere, with further annealing to completely remove all residual damage. While intrinsic amorphous LiNbO3 regrows at temperatures near 400°C, the presence of implanted Ti slows the regrowth and subsequent defect annealing such that temperatures near 1000°C are required. 2 Other transition elements, such as Ag, have been used as dopants in the production of optical waveguides, but they were introduced by thermal diffusion. 3 The purpose of this study was to determine whether such species can be successfully introduced by ion implantation, and whether their effects on the SPE and annealing would offer benefits over the use of Ti. EXPERIMENTAL PROCEDURE Samples of X-cut optical grade LiNbO 3 were implanted at liquid nitrogen temT 45 perature with 360-key Ti or 190-keV "' Ag to doses ranging from 3 x 10'5 to 1 X 101T 2 ions/cm . All implantations produced a highly damaged, essentially amorphous region extending to a depth of about 4000 A, as measured by Rutherford backscattering spectrometry (RBS) of 2-MeV alpha particles along the axial channel normal to the
t Sponsored by the Division of Materials Sciences, U. S. Department of Energy under contract DE-AC05- 840R21400 with Martin Marietta Energy Systems, Inc.
Mat. Res. Soc. Symp. Proc. Vol. 100. ©1988 Materials Research S
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