Schottky barrier effect on the electrical properties of Fe₃O₄/ZnO and Fe₃O₄/Nb : SrTiO₃ heterostructures

Abstract

The current–voltage ( I – V ) characteristics of Fe 3 O 4 /Nb-doped SrTiO 3 (Nb : STO) and Fe 3 O 4 /ZnO junctions prepared by pulsed laser deposition were investigated as a function of temperature. The rectifying behaviour was more distinctive in Fe 3 O 4 /Nb : STO than in the Fe 3 O 4 /ZnO. Contrary to Fe 3 O 4 /Nb : STO, remarkably, the current flow in Fe 3 O 4 /ZnO was slightly larger for negative bias voltages than for positive bias voltages. The threshold voltage in Fe 3 O 4 /Nb : STO dramatically shifted to a higher voltage by decreasing the temperature, and hysteresis behaviour with a cyclic voltage sweep appeared below 120 K. Upon cooling, the rectifying behaviour in Fe 3 O 4 /ZnO gradually disappeared within the measurement range. The observed difference between Fe 3 O 4 /Nb : STO and Fe 3 O 4 /ZnO could be explained by the shape and height of the Schottky barrier which was determined by the relative magnitude of the work functions of the two contact materials. The formation of the Schottky barrier presumably resulted from an upward shift of the interface band in Fe 3 O 4 /Nb : STO, while a little downward shift of the interface band occurred in Fe 3 O 4 /ZnO. In addition, Al-doping into ZnO induced a complete disappearance of the Schottky barrier in the Fe 3 O 4 /Al-doped ZnO junction.