Structural characteristics,impedance spectroscopy,ac-conductivity and dielectric loss studies on RF-magnetron sputtered F doped ZnO (FZO) thin films

The manuscript demonstrates the structural characteristics, impedance spectroscopy, ac-conductivity and dielectric loss studies on F-doped ZnO films grown by RF-magnetron sputtering at T_S ～50 and 125 °C. The electrical impedance spectroscopy enables separately recognizing the contributions of grain and grain-boundary on the electronic properties. The relaxation time distribution on temperature results in the asymmetric and depressed nature of the semi-circular arcs in the Cole-Cole plot and endorses a non-Debye type response under changing electric fields. The negative temperature coefficient of resistance behaviour indicates the semiconducting characteristics. A parallel equivalent circuit model (R || CPE) is designed to fit the semi-circular arc. The grain boundary being more resistive than ZnO-grain, its activation energy appears more significant because of the dynamic disorder characteristics. The ac-conductivity obeys Jonscher power law, and frequency exponent n < 1 suggests hopping of charge carriers with translation motion under ac electric field. The temperature-dependent dc-conductivity follows the Arrhenius behaviour. Sample deposited at higher T_S has a greater carrier lifetime due to the improved crystalline structure and lesser defects. Although, the dielectric loss in the form of conduction loss is higher for the low temperature grown sample owing to the relatively effortless movement of charge carriers and formation of dipoles due to its elevated dc conductivity consequent to increased doping.