Abstract

The present work is focused on the investigation of transport properties of LiNbO3 films synthesized through the crystallization of amorphous coatings as an alternative approach of high-quality films formation. Li–Nb–O amorphous films were deposited onto SiO2–Si substrates by the radio-frequency magnetron sputtering (RFMS) technique in an Ar environment. As-grown films crystallize under thermal annealing (TA) at the temperature of up to 600 °C with a formation of LiNbO3. The Hall effect analysis revealed that electrons are the major carriers in as-grown amorphous films, with the small-polaron hopping as a prime charge transport mechanism. TA in air provokes the increase in the carrier concentration from 6·1011 cm-3 to 6·1014 cm-3, originated from the NbLi antisite defect generation due to Li2O loss. We detected two concurrent transport processes contributing the net Hall mobility: the grain boundary limited and the bulk single-crystal limited mobility. Our results suggest that during the crystallization process, grain boundaries start playing a dominant role in charge transport, whereas when the grains get larger under recrystallization, the bulk single-crystal mobility prevails. The activation energy of the Hall mobility (Eaμ) and conductivity (Eaσ) has been determined for the studied films after TA at various temperatures. Eaμ rises non-monotonically from 0.1 eV with the annealing temperature and reaches a peak of 0.61 eV at a temperature of about 550 °C, which correlates with the trap concentration in LN films after TA. Besides, as followed from our analysis, the Nb4+ defects (electronic traps) are generated at the grain boundaries under TA and after recrystallization the intergranular barriers with the height of 0.5 eV limit the charge transport processes.

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