Fabrication of ZnO films by PLD method with bias voltage

We fabricated ZnO films by pulsed laser deposition (PLD) method with bias voltage to decrease defects in ZnO. The bias voltages of −500 and +500 V were applied between the grid over substrate and the target to control the potential difference between the plume and the target. ZnO films were grown on sapphire (Al2O3) substrates and the substrate temperatures were 20 and 700 °C. Drastic decrease of the integral intensity of deep level emission due to the defects was observed for the films biased with +500 V. On the other hand, deep level emission slightly increased for the films biased with −500 V. The film biased with +500 V had flat surface with hexagonal patterns, which indicated the highly oriented crystal growth. These bias effects were more obvious for the films grown at 700 °C than that grown at 20 °C. These results suggest that applying +500 V bias voltage is effective to obtain highly oriented ZnO crystals with low defects density in PLD. This is probably because the dynamics of Zn2+ particles in plume is controlled by applied bias voltage.