Reasons for obtaining an optical dielectric constant from the Poole–Frenkel conduction behavior of atomic-layer-deposited HfO2 films

The leakage current characteristics of a 16-nm-thick HfO2 film, grown by atomic-layer-deposition using HfCl4 as Hf precursor and O3 as oxidant, were investigated. The electron injection from the Pt top electrode to the HfO2 films was measured at various temperatures. The measured leakage current versus applied bias voltage curves showed the Poole–Frenkel conduction behavior in the high electric field region. However, the estimated dielectric constant from the Poole–Frenkel fitting corresponds to the dielectric constant of the optical frequency region. The quantum mechanical calculation of the electron transition from the metal electrode to the traps in the HfO2 film showed that the transition time was very short (10−14–10−16s) under the applied field. Therefore, the dielectric response of the HfO2 film to the electron conduction by Poole–Frenkel mechanism must be of the optical frequency under steady state current conduction.