[论文解读] Nontrivial temperature behavior of the carrier concentration in the nanostructure "graphene channel on ferroelectric substrate with domain walls"

Anatolii I. Kurchak, Anna N. Morozovska+2 more|arXiv (Cornell University)|Dec 8, 2017

Graphene research and applications参考文献 27被引用 4

一句话总结

本研究揭示了在具有畴壁的铁电衬底上，石墨烯纳米结构中存在非平凡的温度依赖性载流子浓度行为，其中随着温度升高，系统从单重反铁电样滞回环转变为具有不规则、准混沌电压特征的双重反铁电样滞回环。该效应源于石墨烯载流子对铁电极化的非线性屏蔽以及热驱动的畴壁动力学，实现了可调谐的 p-n 结运动，表明其在下一代石墨烯基调制器中具有巨大潜力。

ABSTRACT

This work explores a nontrivial temperature behavior of the carriers concentration, which governs graphene channel conductance in the nano-structure "graphene channel on ferroelectric substrate" that is a basic element for FETs in non-volatile memory units of new generation. We revealed the transition from a single to double antiferroelectric-like hysteresis loop of the concentration voltage dependence that happens with the temperature increase and then exist in a wide temperature range (from 350 to 500 K). Unexpectedly we revealed the double loops of polarization and concentration can have irregular shape that remains irregular as long as the computation takes place, and the voltage position of the different features (jumps, secondary maxima, etc.) changes from one period to another, leading to the impression of quasi-chaotic behavior. It appeared that these effects originate from the nonlinear screening of ferroelectric polarization by graphene carriers, as well as it is conditioned by the temperature evolution of the domain structure kinetics in ferroelectric substrate. The nonlinearity rules the voltage behavior of polarization screening by graphene 2D-layer and at the same time induces the motion of separated domain walls accompanied by the motion of p-n junction along the graphene channel (2D-analog of Hann effect). Since the domain walls structure, period and kinetics can be controlled by varying the temperature, we concluded that the considered nano-structures based on graphene-on-ferroelectric are promising for the fabrication of new generation of modulators based on the graphene p-n junctions.

研究动机与目标

• 研究具有畴壁的铁电衬底上石墨烯沟道中载流子浓度的温度依赖性行为。
• 理解载流子浓度-电压特性中复杂非单调滞回行为的起源。
• 探讨非线性屏蔽与畴壁动力学在调控观测到的输运异常中的作用。
• 评估此类纳米结构在下一代非易失性存储器与可调谐调制器中的可行性。

提出的方法

• 对具有畴壁的铁电衬底上石墨烯沟道的载流子浓度响应进行数值建模。
• 模拟在不同温度与电压条件下，石墨烯中二维电子气对极化率的屏蔽行为。
• 分析畴壁运动及其对石墨烯沟道中 p-n 结空间分布的影响。
• 运用非线性屏蔽理论解释双重滞回环及不规则电压特征的出现。
• 研究畴结构动力学的温度演化及其对电学响应的影响。
• 将模拟的电压依赖性载流子浓度与实验类滞回环进行对比，以验证模型。

实验结果

研究问题

• RQ1 随着温度升高，石墨烯/铁电纳米结构中的载流子浓度-电压滞回行为如何变化？
• RQ2 温度升高导致从单重到双重反铁电样滞回环转变的原因是什么？
• RQ3 为何跳跃点与次级极大值等特征的电压位置在循环中表现出不规则、准周期性移动？
• RQ4 石墨烯载流子对铁电极化的非线性屏蔽如何影响观测到的输运行为？
• RQ5 通过温度调控，畴壁动力学与 p-n 结运动在多大程度上可被控制？

主要发现

• 随着温度升高，载流子浓度中出现从单重到双重反铁电样滞回环的转变，且在宽温区范围（350–500 K）内持续存在。
• 双重滞回环呈现不规则形状，跳跃点与次级极大值等特征的电压位置在循环中不断移动，表明存在准混沌行为。
• 该现象源于二维石墨烯载流子层对铁电极化的非线性屏蔽，该过程与温度依赖的畴壁动力学相耦合。
• 畴壁运动诱导出一种二维版的汉恩效应，其中 p-n 结因动态屏蔽而在石墨烯沟道中发生迁移。
• 温度依赖的畴结构动力学使得电学响应可调谐控制，显著增强了纳米器件的功能性。
• 该系统在基于石墨烯 p-n 结的下一代调制器中展现出巨大潜力，具备可调谐与可切换的输运特性。