Purely hopping conduction in c-axis oriented LiNbO3 thin films

Dielectric constant and ac conductivity of highly c-axis oriented LiNbO3 thin film grown by pulsed laser deposition were studied in a metal-insulator-metal configuration over a wide temperature (200 to 450 K) and frequency (100 Hz to 1 MHz) range. The preferred oriented Al (1%) doped ZnO film with electrical conductivity 1.1 X 10(3) Omega(-1) cm(-1) was deposited for dual purpose: (1) to serve as nucleating center for LiNbO3 crystallites along preferred c-axis growth direction, and (2) to act as a suitable bottom electrode for electrical studies. The room temperature dc conductivity (sigma(dc)) of LiNbO3 film was about 5.34 X 10(-10) Omega(-1) cm-1 with activation energy similar to 0.3 eV, indicating extrinsic conduction. The ac conductivity sigma(ac) was found to be much higher in comparison to sigma(dc) in the low temperature region (<300 K) and exhibits a power law behavior due to the hopping of charge carriers. In higher temperature region (>300 K), sigma(ac) shows a weak frequency dependence, whereas dielectric constant exhibits a strong frequency dispersion. The dielectric dispersion data has been discussed in the light of theoretical models based on Debye type mixed conduction and purely hopping conduction. The dominant conduction in c-axis oriented LiNbO3 thin film is attributed to the purely hopping where both sigma(dc) and sigma(ac) arise due to same mechanism. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3121509]