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基于电子器件小型化、非挥发、低功耗等发展需求，铁电隧道结被认为是最有前景的信息存储器之一。传统钙钛矿铁电薄膜材料在小尺寸下的性能退化是遏制铁电隧道结和相关铁电器件小型化的重要因素。CuInP2S6、In2Se3、HfO2等在原子尺度或数纳米下仍具有稳定铁电性的铁电薄膜的出现，为基于铁电材料的小型化电子器件的发展带来了契机。
Fig. 1 Structuralconfigurations of the heterostructures.
来自湘潭大学材料科学与工程学院的杨琼教授和姜杰副教授团队利用单层厚度的α-In2Se3铁电体和六方IV-VI族半导体(SnTe and PbSe)，设计了一类二维铁电/半导体范德华异质结。第一性原理研究表明，该异质结能够在α-In2Se3铁电极化翻转的调控下，实现从宽带隙绝缘态到金属态的转变。
Fig. 2 Layer-projected band structures of the heterostructures.
基于该类异质结显著的能带调控性质，研究者提出了一种新型的面内二维铁电隧道结。该铁电隧道结以α-In2Se3/IV-VI族半导体异质结为势垒区、以重电子掺杂的异质结作为虚拟电极。
Fig. 3 Schematic of the electrostaticpotential and band alignment.
由于α-In2Se3面内、外协同的铁电极化，可以通过施加面内或面外的电场控制铁电隧道结整个势垒区的极化状态和电子能带结构，从而实现隧道结的开和关态。该铁电隧道结并非依靠传统的界面非对称性来调控电子隧穿势垒，因而也不依赖于电极的类型。
Fig. 4 Structuralconfigurations of the FTJ.
研究表明，设计的平面铁电隧道结的开/关状态呈现金属导电和电子隧穿两种截然不同的导电机制，从而达到1 ´ 104以上的关/开电阻比，且其电致电阻效应随着势垒宽度的增加而显著增加。该类异质结也可以用于面外铁电隧道结。
Fig. 5 The partial charge densities of the FTJ.
In-plane ferroelectric tunnel junctions based on 2D α-In2Se3/semiconductor heterostructures
Zifang Liu, Pengfei Hou, Lizhong Sun, Evgeny Y. Tsymbal, Jie Jiang & Qiong Yang
Ferroelectric tunnel junctions (FTJs) have great potential for application in high-density non-volatile memories. Recently, α-In2Se3 was found to exhibit robust in-plane and out-of-plane ferroelectric polarizations at a monolayer thickness, which is ideal to serve as a ferroelectric component in miniaturized electronic devices. In this work, we design two-dimensional van der Waals heterostructures composed of an α-In2Se3 ferroelectric and a hexagonal IV-VI semiconductor and propose an in-plane FTJ based on these heterostructures. Our first-principles calculations show that the electronic band structure of the designed heterostructures can be switched between insulating and metallic states by ferroelectric polarization. We demonstrate that the in-plane FTJ exhibits two distinct transport regimes, tunneling and metallic, for OFF and ON states, respectively, leading to a giant tunneling electroresistance effect with the OFF/ON resistance ratio exceeding 1 104. Our results provide a promising approach for the high-density ferroelectric memory based on the 2D ferroelectric/semiconductor heterostructures.
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