Enhancing the dielectric constant of oxides via acceptor-donor co-doping

Aiming to enhance the dielectric constant and maintaining a relatively low dielectric loss, transparent acceptor-donor (Cu-Ga) co-doped ZnO films were fabricated on c-sapphire using pulsed laser deposition. With Ga=0.5 wt% and Cu=8 wt%, the dielectric constant was optimised while the dielectric loss is relatively low ( 204 and 0.27 respectively at the frequency of 1 kHz). The dielectric constant is stable over a wide range of frequency of ~10-106 Hz. The film has good optical transmittance (>75 %) in the visible wavelength range (450-800 nm). Ac conductivity study reveals two relaxation processes in the sample, namely the correlated barrier hopping (CBH) and the small polaron tunneling (SPT). The enhancement of the dielectric constant was ascribed to the formation of new defect complexes induced by the acceptor-donor doping; and the CBH and SPT of electrons between these neighboring defect complexes.