Effect of cation and anion defects on the resistive switching polarity of ZnO x thin films

In this paper, we achieve the resistive switching (RS) polarity from unipolar to bipolar in a simple Al/ZnO (x) /Al structure by moderating the oxygen content in the ZnO sputtering process. In a pure Ar sputtering, Al/ZnO (x) /Al shows unipolar behavior, as oxygen partial pressure increases, the RS polarity changes to bipolar, and the switch current decreases by about five orders of magnitude. The current transport properties of unipolar device show ohmic behavior under both high resistance (HRS) and low resistance states (LRS), but the bipolar device shows Schottky barrier modulated current transport properties. We study the defect types in the unipolar and bipolar devices through photoluminescence (PL) spectra. The PL results show that the interstitial zinc (Zn-i) and interstitial oxygen (O-i) are dominant in unipolar and bipolar devices, respectively. We attribute this phenomenon to Zn-i and O-i playing important role in unipolar (URS) and bipolar resistive switching (BRS), respectively.