Transport properties and crystallization of Li–Nb–O system on silicon

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.