Proton Effects in KTiOPO 4
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PROTON EFFECTS IN KTiOPO4 P. A. MORRIS, M. K. CRAWFORD, M. G. ROELOFS, J. D. BIERLEIN E. I. du Pont de Nemours & Co., Experimental Station, Wilmington, DE 19880 P. K. GALLAGHER, AT & T Bell Laboratories, 600 Mountain Ave., Murray Hill, NJ 07974 G. GASHUROV, Airtron, Litton Systems, Inc., E. Hanover Ave., Morris Plains, NJ 07950 G. M. LOIACONO*, Philips Laboratories, Scarborough Rd., Briarcliff Manor, NY 10510 ABSTRACT Evidence supporting the temperature dependent defect mechanism of nonstoichiometry on the potassium and oxygen sublattices in KTP is presented. The primary compensating defects for the formation of vacant potassium sites in typical flux grown KTP are vacant oxygen sites. Protons (OH-) are the principal defect compensating for the formation of vacant potassium sites in high temperature hydrothermal KTP. A model of the ionic conductivity in high temperature hydrothermal KTP is proposed in which specific protons participate in cooperative motion over a limited distance with the potassium vacancies migrating along the "channels" in the structure in the Z-direction. The higher activation energy measured for ionic conductivity in flux grown KTP (0.5 eV) relative to high temperature hydrothermal (0.3 eV) is suggested to be due to the energy required to dissociate from a defect complex, such as a (VO - VK). The correlation of ionic conductivity to damage susceptibility appears to be due to the levels of compensating defects for vacant potassium sites in KTP, which are related to the concentrations of Ti 3 + formed in the crystals. Further study is ongoing to understand the specific mechanisms involved in the ionic conductivity and damage in KTP grown by the flux and hydrothermal techniques. INTRODUCTION KTP possesses a unique combination of properties making it a superior nonlinear crystal for second harmonic generation and electro-optic applications. [1-3] Recent work indicates that
KTP may also be useful for parametric generation. [4] The techniques presently used to grow
KTP include high and low temperature hydrothermal and submerged and top seeded flux. [5-11] Melt growth techniques are not used because KTP decomposes upon melting. [8] The linear, nonlinear and electro-optic coefficients of KTP crystals grown by the hydrothermal and flux techniques are similar, but differences have been observed in the low frequency dielectric properties and damage characteristics. [3,121 The ionic conductivity is important in the processing of waveguides in the material and to waveguide device stability. [3,13] Damage in KTP can be produced optically, with electric fields or hydrogen annealing and is attributed to Ti3 + formation in the crystal. [14-16] Our previous work [121 on the defects present in KTP as a function of the growth technique resulted in the following proposals: 1) nonstoichiometry exists on the K and 0 sublattices in KTP, increasing in magnitude with the growth temperature, 2) OH- present in specific sites in hydrothermally grown KTP has an effect on the ionic conductivity and damage susceptibility, a
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