Degradation of the Acousto-Electric Current Saturation Behavior in C-Axis Fiber-Textured Polycrystalline Zinc Oxide Films

Acousto-electric current saturation has been observed in thin, polycrystalline Al-doped zinc oxide films grown on fused quartz. The films, grown by laser ablation, are c-axis textured with high angle grain boundaries between the grains. After annealing at 600°C in 0.1 mtorr oxygen, the films exhibit a current saturation at a current density of 2 105 A/cm2 and electric fields of 5 103 V/cm. However, under constant field the current density falls and the current saturation behavior is not maintained. Current saturation at the same current density can, however, be restored by increasing the electric field. Similarly, the appearance and disappearance of the current saturation behavior can be reversibly controlled by annealing in different oxygen partial pressures at 200°C. The degradation phenomena is attributed to the high acoustic flux enhancing the diffusion of oxygen along the grain boundaries where oxygen can alter the grain boundary potential barrier and hence the electric field in the grains.