Electrical characteristics and stability of gold and palladium Schottky contacts on ZnO nanorods

The electrical characteristics and stability of Pd and Au Schottky contacts on ZnO nanorods grown on glass substrate have been investigated. The nanorods were grown using the aqueous chemical growth method. The nanorods were characterized with scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL). Prior to the metal contact deposition, an insulating PMMA layer was deposited between the nanorods. The best-produced Schottky contact was an as-deposited Pd/ ZnO contact with an ideality factor of 1.7 +/- 0.43 and a barrier height of 0.67 +/- 0.09 eV. The relatively high ideality factor indicates that the current transport cannot be described by pure thermionic transport. The presence of surface states due to the high evaporation pressure is probably the reason for the high ideality factor. Post metal deposition annealing at 150 degrees C for 30 min in air lowered the barrier height and decreased the Au/ ZnO ideality factor but increased it for Pd/ ZnO. The current follows ohmic behavior when the applied forward bias, V-forward, is lower than 0.1 V, whereas for Vforward between 0.1 and 0.45 V the current follows I similar to exp(cV), and at higher forward biases the current-voltage characteristics follow the relation I similar to V-2, indicating that the space-charge current-limiting mechanism is dominating the current transport.