Conduction mechanism in amorphous rf-sputtered TeO2+y thin films

The wide range temperature (150 K to 470 K) and frequency (100 Hz to 1 MHz) dependence of the dielectric constant and ac conductivity of rf-sputtered TeO2+y thin films (y = 0 to 1) deposited in metal-insulator-metal configuration is studied. A decrease in the value of the dc conductivity measured at room temperature was observed with increasing y, whereas the ac conductivity and dielectric constant show an increasing trend. The values of the dielectric constant for temperatures more than 340 K were found to depend intensely on the frequency because of the intrinsic behavior of the films. The dielectric distribution data have been analyzed in terms of (i) a mixed conduction model (with a spread of relaxation times) and (ii) a random free energy barrier model (which assumes that the conduction mechanism is hopping, and the dielectric spread is correlated with dc conductivity). The reason for the dielectric spread has been discussed on the basis of these models. It has been observed that the dominant transport mechanism in TeO2+y film is purely hopping in the low temperature region (<340 K) and mixed conduction at high temperature (>340 K).