Characterization of surface layers in Zn-diffused LiNbO₃ waveguides by heavy ion elastic recoil detection

The surface layers formed in LiNbO₃ waveguides, fabricated by Zn diffusion from the vapor phase, have been investigated by time of flight elastic recoil detection analysis using ¹²⁷I ions. The key features of this technique, simultaneous profiling of all ions and a depth of analysis ≪1 μm, have allowed a detailed and quantitative characterization of the surface layers. The Zn diffusion into LiNbO₃ can be understood as a 2Li↔Zn exchange process. As a consequence, an outermost layer of several hundreds of nanometers is formed, consisting of LiNbO₃ and ZnNb₂O₆ phases showing complementary profiles. A good correlation has been found between the composition profiles and the optical waveguiding behavior. After thermal annealing of the waveguides, a thinner layer containing a uniform mixture of ZnO and LiNbO₃ is generated followed by a transition to a graded solid solution of Zn into LiNbO₃. © 2002 American Institute of Physics.