Electrical characteristics and stability of gold and palladium Schottky contacts on ZnOnanorods

Abstract

The electrical characteristics and stability of Pd and Au Schottky contacts on ZnOnanorods grown on glass substrate have been investigated. The nanorods were grown usingthe aqueous chemical growth method. The nanorods were characterized with scanningelectron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL).Prior to the metal contact deposition, an insulating PMMA layer was depositedbetween the nanorods. The best-produced Schottky contact was an as-depositedPd/ZnO contact with anideality factor of 1.74 ± 0.43 and a barrier height of 0.67 ± 0.09 eV. The relatively high ideality factor indicates that the current transport cannot be describedby pure thermionic transport. The presence of surface states due to the high evaporationpressure is probably the reason for the high ideality factor. Post metal deposition annealing at150 °C for 30 min in air lowered the barrier height and decreased theAu/ZnO ideality factor butincreased it for Pd/ZnO. The current follows ohmic behavior when the applied forward bias,Vforward, is lower than0.1 V, whereas for Vforward between 0.1 and 0.45 V the current followsI∼exp(cV), and at higher forward biases the current–voltage characteristics follow the relationI∼V2, indicating that the space–charge current-limiting mechanism is dominating the currenttransport.