Characterization of charge trapping in Eu doped Al$_{2}$O$_{3}$ and its application to a nonvolatile memory.

Charge trapping and luminescence properties of Eu ions at different charge states have been investigated for Eu-doped-Al$_{2}$O$_{3}$/SiO$_{2}$/Si structure. X-ray photoelectron spectroscopy and photoluminescence spectra studies showed that doped Eu ions mainly exist in Eu$^{3+}$ state for samples annealed at low temperature. When charges were injected by Fowler-Nordheim tunneling, Eu doped Al$_{2}$O$_{3}$ layer showed a strong electron trapping behavior. After high temperature thermal annealing in reducing ambient gas, the luminescence spectra changed into those of Eu$^{2+}$. However, charge trapping was negligible. Our experimental results indicate that Eu$^{3+ }$ion in Al$_{2}$O$_{3}$ behaves as a strong electron trap while Eu$^{2+ }$ion formed after high temperature thermal annealing behaves as a strong luminescent center. As an application, we fabricated a non-volatile memory MOS structure using Eu doped Al$_{2}$O$_{3}$ as a charge trapping layer and obtained good memory properties.