Ion implantation into LiNbO3

Abstract LiNbO3-crystals are of great importance for the formation of integrated optical elements and devices. Ion irradiation can be used to modify the refractive index in well defined regions and, consequently, to produce waveguide structures in surface layers. The investigation of radiation damage and its influence on significant physical properties such as refractive indices n0 and ne, density and etching rate is of great importance for solving this problem. The change of the refractive index caused by radiation damage is well determined by the energy density deposited in nuclear processes. Therefore the dependence on the ion dose D can be discussed for one ion species. Results for the implantation of 150 keV nitrogen ions into LiNbO3 (X-, Y- and Z-cuts) show that the change of the physical properties can be divided into three regions of the damage: 1. (1) D⩽1×1015 N+/cm2: predamage stage - generation of point defects; up to 30% of the Nb-atoms are distributed on vacant octahedral lattice sites. 2. (2) 1×1015 3. (3) D⩾5×1015 N+/cm2: saturation stage - saturation of the damage; change of the density up to about 11%; drastic enhancement of the etching rate; saturation of the change of the extraordinary refractive index, but preserving an anisotropy ne − n0 of 60% of the value of crystalline LiNbO3.