Tunneling-assisted Poole-Frenkel conduction mechanism in HfO2 thin films

Tunneling-assisted Poole-Frenkel (TAPF) mechanism, which represents electron tunneling from a metal electrode to traps in a nearby insulator layer followed by detrapping of the electrons from the traps by virtue of a lowered potential well due to an applied electric field, is suggested in this study to precisely describe the electrical conduction behavior of a Pt∕HfO2∕Si capacitor. The current density versus the applied electric-field curves of the TAPF conduction show a similar electric-field dependency to that of the Poole-Frenkel (PF) conduction. However, unlike the PF mechanism, the activation energy of the leakage current density corresponds to the value of the Schottky barrier height (SBH) of a metal/insulator junction minus a lowered potential-well height by the applied electric field in the TAPF mechanism. In addition, the SBH of the Pt∕HfO2 junction is calculated considering a high space-charge density (>∼1018cm−3) in the HfO2 layer. The measured activation energy for the electrical conduction from an atomic-layer-deposited HfO2 film is compared to the value that is expected from this model.