Charge trapping defects in film stacks characterized by spectroscopic second-harmonic generation
(Color online) Spectroscopic TD-EFISH results for as-deposited . A unique decay in the SHG intensity is evident for incident photon energies .
(Color online) Second-harmonic phase measurements from as-deposited . The overlapping interferograms were measured at three different times during the TD-EFISH measurement and indicate that the second-harmonic phase is not changing.
(Color online) EFISH decay amplitude vs incident photon energy at fixed laser power for as-deposited , showing resonant enhancement near 1.62 eV. Red squares represent experimental data. Curves are Lorentzian functions representing a sharp resonance at 1.62 eV (dashed), an interband absorption tail (dotted), and the composite line shape (solid) that is fit to the data.
(Color online) TD-EFISH results for as-deposited as a function of incident laser power. The inset is a log-log plot of EFISH decay rate vs incident laser power.
(Color online) TD-EFISH hysteresis results from as-deposited . Scan #1 was recorded using the virgin as-deposited sample. Scan #2 was recorded after Scan #1 with the laser on the same spot on the sample, after removing accumulated surface charge with the laser temporarily blocked.
(Color online) Schematic band diagram representation of the different charge transport mechanisms leading to the TD-EFISH results. The localized 3.24 eV defect within the HfO2 layer is believed to be responsible for the EFISH decay.
EFISH decay can be suppressed by increasing the SiO2 interfacial layer to 2 nm.
(Color online) Spectroscopic TD-EFISH results for annealed HfO2. Only a monotonically increasing SHG signal is observed for all incident photon energies.
(Color online) TD-EFISH hysteresis results from annealed HfO2.
(Color online) Spectroscopic TD-EFISH results for the as-deposited Hf-silicate films ( , , and ). Only a monotonically increasing SHG signal is observed for all incident photon energies.
(Color online) Capture cross sections for all samples as a function of three photon energy.
(Color online) TD-EFISH hysteresis measurements for all as-deposited Hf-silicate films ( , , and ).
Lifetime of the trapped negative surface charge is investigated for each as-deposited Hf-silicate film by temporarily blocking the laser and allowing for the accumulated charge to de-trap. (a) The 20% silicate film exhibits a long surface trap lifetime similar to the samples, while the 40% (b) and 60% (c) silicate films have significantly shorter trapped charge lifetimes.
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