Nanocomposites and nanomaterials

The processes of diffusion and drift of copper ions in LiNbO3 crystal
U. Yakhnevych 1, D. Sugak 1,2, I.I. Syvorotka 1,2, O. Buryy 1, Ya. Zhydachevskyy 1,3, S. Ubizskii1, A. Suchocki 3,4 
1 Department of Semiconductor Electronics, Lviv Polytechnic National University, 12, Bandera Str.,79000 Lviv, Ukraine. 
E-mail: yakhnevych.u@gmail.com
2 Scientific Research Company “Electron-Carat”, 202 Stryjska st., 79000 Lviv, Ukraine
3 Institute of Physics PAS, 32/46 Al. Lotników, Warsaw, Poland
4 Institute of Physics, Kazimierz Wielki University, 11 Weyssenhoffa st., Bydgoszcz, Poland

High temperature annealing of lithium niobate (LiNbO3) in the presence of metal ions is one of the techniques which is extensively used to create LiNbO3-based elements for acoustoelectronics, optoelectronics and integrated optics. The diffusion doping of LiNbO3 by Cu is successfully used for increasing of the photorefractive sensitivity of this crystal. In this work we studied the Cu diffusion in LiNbO3 by optical spectroscopy. The Cu film was deposited on one surface of the crystal before thermal treatment. Each sample was annealed at T = 873, 923, 973, 1023 and 1073 K during 6 hours. The optical absorption spectra of the samples were recorded in a direction perpendicular to the direction of diffusion at different distances from the crystal edge. The absorption bands of Cu+ (400 nm) and Cu2+ (1100 nm) ions are observed in all annealed samples. The distributions of the concentrations of the incorporated copper ions were calculated in accordance with Smakula-Dexter formula [1]. The depth dependencies of Cu ions concentrations were approximated in frames of the model taking into account both the diffusion and the drift of Cu ions. The diffusion coefficients determined from the approximations are in good agreement with the ones known from literature. It was also shown that the absorption spectra in the region near 400 nm consist of at least two bands with the intensities varying in different ways if the distance from the crystal surface is changed.
As a conclusion, it should be noted that the character of the Cu ions spatial distribution is determined by the complex process including the Cu  Li ions exchange, the Cu+  Cu2+ ions recharging and their interaction with point defects of the crystal lattice, particularly the ones that compensate the excess charge of Cu2+. Acknowledgements: the work was supported by the Ukrainian Ministry of Education and Science (project DB/MEZHA no. 0118U000273).

1.	Dexter D.L. Absorption of Light by Atoms in Solids // Phys.Rev.–1956.–101.-P. 48–55.