Ion Implantation and Ion Beam Analysis of Lithium Niobate
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ION IMPLANTATION AND ION BEAM ANALYSIS OF LITHIUM NIOBATE G. W. ARNOLD Sandia National Laboratories, Ion-Solid Interactions Division 1111, Albuquerque, NM 87185-5800 ABSTRACT Implantations of He and Ti were made into LiNbO 3 and the H and Li profiles determined by elastic recoil detection (ERD) techniques. The loss of Li and gain of H depends upon the supply of surface H (surface contaminants or ambient atmosphere). For 50 keV He implants into LiNbO 3 through a 200 K Al film, the small Li loss is governed by the interface H. This is also the case for He implants into uncoated LiNbO 3 in a beam line with low hydrocarbon surface contamination; similar implants under conditions of greater hydrocarbon deposition result in proportionally larger Li loss and H gain in the implant damage region. The exchange is possible only for those He energies, i.e., 50 keV, where the damage profile intersects the surface. For Ti implants Li is lost with little H gain. For this case the Li loss is believed to result from radiation-enhanced diffusion. Where He implantation is used to establish waveguiding in LiNbO 3 , the presence or absence of H in the implanted region is crucial with regard to refractive index stability, due to the replacement of H by Li from the bulk. INTRODUCTION One of the means of establishing waveguiding in LiNbO 3 is ion implantation [1-4]. It has the advantage over proton-exchange (PE) and Ti-diffusion in that it is a low-temperature (< 100*C), relatively fast (depending on beam current) procedure, and lends itself to standard planar technology techniques. There are, however, some questions concerning the composition of the material after implantation and the index stability. These concerns are also common to the PE method [5] and have been addressed in previous work [6]. Elastic recoil detection (ERD) techniques were used in that work [6] to measure H and Li profiles after PE and their changes with time, temperature, and crystallographic orientation. H was found to replace Li in a 1:1 ratio and index instabilities were clearly due to the exchange, with time, of H in the exchange region with Li from the bulk. Previous work on He implantation [4] has shown that 50 keV He implants into LiNbO3 can result in Li loss from the damage region due to interchange with incumbent surface H. This effect was noted only for 50 keV implants, where the damage profile intersects the surface, but not for 800 keV He implants where this is not the case. The near-surface extraordinary index, for implantations with 50 keV He, decreased at low fluences (< 1 x 1016 He/cm 2 ) due to damage-induced positive lattice dilatation and increased at higher fluences due to the increasingly dominant effect of the simultaneously occurring Li loss. At higher He energies, where Li loss is not observed, most of the lattice damage is located at the end of the ion track. This lowered index region allows light to be trapped in the higher index region between the end of the track and the surface. The electronic energy deposition along the ion track has no
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