Swift heavy ion irradiation induces enhancement in electrical conductivity of LiTaO3 and LiNbO3 crystals

Swift heavy ion irradiations (SHI) of insulators have long been known to create macroscopic structural modifications such as a buried damage layer in bulk, due to the ion energy loss, being thus an attractive method to produce optical waveguides in LiNbO3. In this work, we have investigated and related the results from the optical waveguide characterization to the changes in electrical conductivity due to damage by SHI in LiTaO3 and LiNbO3 single crystals. Irradiation with Br ions, with an energy of 40 MeV and fluences within (0.5-10) x 10(13) ions/cm(2), is used to carry out a study of damage accumulation in the buried layer. The changes in the electrical behaviour of the Al- (LiTaO3/LiNbO3] interface and the dependence of conductivity with temperature in the damaged layer, for fluences close to the amorphization threshold in individual tracks, are reported. The DC electrical measurements, between 295 and 420 K, using the two-point probe method were used to characterize the electrical conductivity of the irradiation area. The I-V characteristic of the electrical contacts reveals an ohmic behaviour for both crystals. Measurements of the electrical conductivity at different temperatures in the investigated range suggest a band conduction mechanism thermally activated, with energies of approximately 0.55 eV for both crystals, that is almost independent of the amount of both intrinsic and extrinsic defects that are accumulated when the fluence increases. In addition, the resistance values are larger in LiTaO3 crystals than in LiNbO3 ones for the same fluence.