Local Chemical Origin of Ferroelectric Behavior in Wurtzite Nitrides

Keisuke Yazawa, John Mangum, Prashun Gorai, Geoff Brennecka, Andriy Zakutayev

Research output: Contribution to journalArticlepeer-review

14 Scopus Citations

Abstract

Ferroelectricity enables key modern technologies from non-volatile memory to precision ultrasound. The first known wurtzite ferroelectric Al1−xScxN has recently attracted attention because of its robust ferroelectricity and Si process compatibility, but the chemical and structural origins of ferroelectricity in wurtzite materials are not yet fully understood. Here we show that ferroelectric behavior in wurtzite nitrides has local chemical rather than extended structural origin. According to our coupled experimental and computational results, the local bond ionicity and ionic displacement, rather than simply the change in the lattice parameter of the wurtzite structure, is key to controlling the macroscopic ferroelectric response in these materials. Across gradients in composition and thickness of 0 < x < 0.35 and 140-260 nm, respectively, in combinatorial thin films of Al1−xScxN, the pure wurtzite phase exhibits a similar c/a ratio regardless of the Sc content due to elastic interaction with neighboring crystals. The coercive field and spontaneous polarization significantly decrease with increasing Sc content despite this invariant c/a ratio. This property change is due to the more ionic bonding nature of Sc-N relative to the more covalent Al-N bonds, and the local displacement of the neighboring Al atoms caused by Sc substitution, according to DFT calculations. Based on these insights, ionicity engineering is introduced as an approach to reduce coercive field of Al1−xScxN for memory and other applications and to control ferroelectric properties in other wurtzites.

Original languageAmerican English
Pages (from-to)17557-17566
Number of pages10
JournalJournal of Materials Chemistry C
Volume10
Issue number46
DOIs
StatePublished - 12 Oct 2022

Bibliographical note

Publisher Copyright:
© 2022 The Royal Society of Chemistry.

NREL Publication Number

  • NREL/JA-5K00-84694

Keywords

  • chemical bonds
  • coercive force
  • ferroelectric materials
  • nitrides
  • zinc sulfide

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