Modification of the electronic structure and the electrical properties of ZnO thin films by nickel-ion irradiation at room temperature

Abstract

Radio-frequency (RF) sputtered ZnO films were investigated as a function of the Ni-ion irradiation dose at room temperature. The prepared ZnO films were irradiated with Ni-ions at an acceleration energy of 130 MeV in the dose range from 5 × 1011 ions/cm2 to 1 × 1013 ions/cm2. The electrical properties of the irradiated ZnO films changed with changing Ni-ion irradiation dose. In order to explain the change in the electrical properties of ZnO films, we investigated the physical properties and the electronic structure, such as the physical structure, the molecular orbital in the conduction band, and the band edge state below the conduction band. The physical structure and the physical composition showed no changes, regardless of the Ni-ion irradiation dose. On the other hand, the electronic structure showed a drastic modification of the hybridized molecular orbital ordering of the Zn 4sp and the O 2p in the conduction band. In addition, two distinct band edge states below the conduction band were observed with increasing Ni-ion irradiation dose. These remarkable changes in the electronic structure could be correlated to changes in the electrical properties.