In-plane rotation and transition from rectification to bipolar resistive switching in ZnO/SrTiO3:Nb heterojunctions by substrate pretreatment

The growth behavior and electrical transport properties of ZnO films was found to be strongly dependent on the deionized water soaking treatment of 0.7 wt% (111) SrTiO3:Nb substrates. Comparing the ZnO films on soaked SrTiO3:Nb substrates with those on unsoaked ones, the out-of-plane orientation of ZnO films are both along the c-axis, while there is an in-plane rotation of ZnO thin films. According to the variable frequency capacitance-voltage measurements, a much higher interface state density is found in the ZnO/soaked-SrTiO3:Nb heterojunction than that in the ZnO/unsoaked-SrTiO3:Nb heterojunction. Moreover, a rectification and bipolar resistive switching effect were observed in the ZnO/unsoaked-SrTiO3:Nb and ZnO/soaked-SrTiO3:Nb heterojunctions, respectively. The transition from rectification to a bipolar resistive switching effect can be ascribed to an increase of oxygen vacancies, the migration of which plays an important part in the resistive switching.