Nitrogen Vacancies Induce Fatigue in Ferroelectric Al_0.93B_0.07N.

Area of Science:

• Materials Science
• Solid State Physics
• Device Physics

Background:

• Wurtzite ferroelectrics like Al_0.93B_0.07N offer potential for high-temperature memory applications due to large remanent polarization and stability.
• Current Al_0.93B_0.07N devices exhibit insufficient endurance lifetimes for next-generation computing architectures.

Purpose of the Study:

• To identify the specific defects limiting the endurance of Al_0.93B_0.07N ferroelectric devices.
• To understand the defect evolution mechanisms during ferroelectric switching cycles.

Main Methods:

• Combined electronic measurements and optical spectroscopies to characterize defect states.
• Photoluminescence spectroscopy and positive-up negative-down (PUND) measurements to quantify polarization and defect transitions.
• Thermally stimulated depolarization current and modulus spectroscopy to further analyze defect behavior.

Main Results:

• Identified an emerging optical transition near 2.1 eV during ferroelectric switching, correlating with nonswitching polarization.
• Observed strengthening of this 2.1 eV transition with cycling, indicating an increase in defect states.
• Ascribed the 2.1 eV transition to nitrogen vacancies interacting with deeper bandgap defects.

Conclusions:

• Ferroelectric switching in Al_0.93B_0.07N generates nitrogen vacancies, likely via hot-atom damage from high switching fields.
• This defect generation mechanism is the primary cause of limited endurance in these ferroelectric memory devices.