Ion Implantation of KnbO 3 and LiNbO 3 at Elevated Temperatures
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ION IMPLANTATION OF KNbO AND LiNbO3 AT ELEVATED TEMPERATURES CH.
BUCHAL*,
R. IRMSCHER* and P. GUNTER**
KFA-ISI, D-5170 Jilich, W. Germany ETH H6nggerberg, CH-8093 ZUrich, Switzerland ABSTRACT Ion implantation, annealing and channeling of single crystalline samples of KNbO 3 and LiNbO3 have been studied. Raising the substrate temperature above 600 K, greatly increases the tolerance of the crystals for high-dose implantation. In LiNbO3 dynamic recrystallization has been observed for the first time. INTRODUCTION Oxide ceramic single crystals are very important for optical applications. They are needed for the fabrication of modulators, switches and other integrated optics devices . Their range of applications for linear and nonlinear optics is wide and rapidly growing. A recent review is found in Ref. 1. A general prerequisite for device fabrication is the formation of an optical waveguide within the material. This is a region of enhanced optical index, which acts as a "light guide". Typically, microfabrication processes, as in use for microelectronics are transferred to oxide substrates for waveguide patterning. At this point, each material develops a surprisingly different response and this paper is concerned with the ion implantation properties of KNb0 3 , a strongly nonlinear material and LiNb0 3 , which now has become the workhorse for linear electrooptic and acoustooptic devices. LiNbO3 is available commercially in large high quality wafers and it permits the application of in-diffusion or ion exchange techniques for local alterations of its optical indices (see Ref. 2 for a review). Also implantation of light ions has been studied extensively [3,4] and direct implantation of high doses of Ti for optical index enhancement has been used for optical device fabrication [5,6,7]. This tolerance for diffusion or high dose implantation together with its high Curie temperature of approx. 1400 K make LiNbO3 a unique electrooptical material.
Mat. Res. Soc. Symp. Proc. Vol. 128.
1989 Materials Research Society
720
THE STRUCTURE OF KNbO 3 AND LiNbO3 KNbO 3 crystallizes in the Perovskite structure with an almost cubic cell with K+ ions at the corners, 02- ions on the six faces and one Nb5+ ion near the center. Using Pauling's ionic radii, the lattice may be constructed from close-packed (111) planes, containing a uniform pattern of large K+-ions, surrounded by six 0 2 - ions of equal size (i.e.: 3 02- for each K+). Between the hcp planes, small Nb5 + ions are inserted into octahedral positions between 6 02- ions [1,5]. Any diffusion of K+ ions requires 02- vacancies and vice versa, 02- diffusion is hampered by K+ ions within this hcp sublattice. The LiNbO3 structure is somewhat related, since it also 5 2 consists of close-packed planes of large O -ions. The small Nb + ions and the small Li+ ions move into the numerous available octahedral positions, which really are interstitials within the oxygen sublattice [5,8]. Therefore the lattice of the large ions (02-) is uninterrupted by cations. If vacancies in the 02sublat
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