Local chemical origin of ferroelectric behavior in wurtzite nitrides
Local chemical origin of ferroelectric behavior in wurtzite nitrides
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DOI：
10.1039/d2tc02682a
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发表时间：
2022-10-12
影响因子：
6.4
通讯作者：
Zakutayev, Andriy
中科院分区：
文献类型：
--
作者：
Yazawa, Keisuke;Mangum, John S.;Zakutayev, Andriy
铁电性使从非易失性存储器到精密超声的关键现代技术成为可能。第一个已知的纤锌矿铁电体Al 1-xScxN最近引起了人们的注意，因为其强大的铁电性和Si工艺兼容性，但在纤锌矿材料的铁电性的化学和结构起源尚未完全理解。在这里，我们表明，在纤锌矿氮化物的铁电行为有本地的化学，而不是扩展的结构起源。根据我们耦合的实验和计算结果，本地键离子性和离子位移，而不是简单的纤锌矿结构的晶格参数的变化，是关键控制这些材料的宏观铁电响应。在Al 1-xScxN的组合薄膜中，分别跨越0 < x < 0.35和140-260 nm的组成和厚度梯度，由于与相邻晶体的弹性相互作用，纯纤锌矿相表现出类似的c/a比，而与Sc含量无关。的矫顽场和自发极化显着降低与Sc含量的增加，尽管这个不变的c/a比。根据DFT计算，这种性质的变化是由于Sc-N相对于更共价的Al-N键具有更强的离子键性质，以及由Sc取代引起的相邻Al原子的局部位移。基于这些见解，引入离子性工程作为一种方法，以减少矫顽场的Al 1-xScxN的存储器和其他应用，并控制铁电性能在其他纤锌矿。
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.