Tuning of Plasmons in Transparent Conductive Oxides by Carrier Accumulation,ACS Photonics

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Tuning of Plasmons in Transparent Conductive Oxides by Carrier Accumulation
ACS Photonics ( IF 6.5 ) Pub Date : 2018-02-14 00:00:00 , DOI: 10.1021/acsphotonics.7b01517
Xiaoge Liu ₁ , Ju-Hyung Kang ₁ , Hongtao Yuan _{1,

2,

3} , Junghyun Park ₁ , Yi Cui _{1,

2} , Harold Y. Hwang _{1,

2} , Mark L. Brongersma ₁

Affiliation

A metal naturally displays dramatic changes in its optical properties near the plasma frequency where the permittivity changes from a negative to a positive value, and the material turns from highly reflective to transparent. For many applications, it is desirable to achieve such large optical changes by electrical gating. However, this is challenging given the high carrier density of most metals, which causes them to effectively screen externally applied electrical fields. Indium tin oxide (ITO) is a low-electron-density metal that does afford electric tuning of its permittivity in the infrared spectral range. Here, we experimentally show the tunability of the plasma frequency of an ITO thin film by changing its sheet carrier density via gating with an ionic liquid. By applying moderate gate bias values up to 1.4 V, the electron density increases in a thin (∼3 nm) accumulation layer at the surface of the 15-nm-thick ITO film. This results in notable blue shifts in the plasma frequency. These optical and electrical changes are monitored simultaneously, which facilitates construction of a model that provides a consistent picture for the dc electrical and infrared optical properties. It can be used to quantitatively predict the optical changes in the ITO layer with applied bias. This work builds our understanding of electrically tunable plasmonic materials and aids the design of ultracompact, active nanophotonic elements.

中文翻译：

通过载流子积累来调节透明导电氧化物中的等离激元

金属自然在等离子频率附近显示出光学特性的戏剧性变化，在该频率下，介电常数从负值变为正值，材料从高反射率变为透明。对于许多应用，希望通过电选通实现如此大的光学变化。但是，鉴于大多数金属的高载流子密度，这极具挑战性，这使它们能够有效地屏蔽外部施加的电场。氧化铟锡（ITO）是低电子密度的金属，确实可以在红外光谱范围内对其介电常数进行电调谐。在这里，我们通过用离子液体进行浇铸来改变其薄膜载流子密度，从而实验性地显示了ITO薄膜的等离子体频率的可调谐性。通过施加高达1.4 V的中等栅极偏置值，电子密度在厚度为15 nm的ITO膜表面的一个薄的（〜3 nm）累积层中增加。这导致等离子体频率出现明显的蓝移。同时监视这些光学和电气变化，这有助于构建模型，从而为直流电和红外光学特性提供一致的图像。它可用于定量预测施加的偏压下ITO层中的光学变化。这项工作建立了我们对电可调等离子体材料的理解，并有助于设计超紧凑的活性纳米光子元件。这有助于构建模型，从而为直流电和红外光学特性提供一致的图像。它可用于定量预测施加的偏压下ITO层中的光学变化。这项工作建立了我们对电可调等离子体材料的理解，并有助于设计超紧凑的活性纳米光子元件。这有助于构建可为直流电和红外光学特性提供一致图像的模型。它可用于定量预测施加的偏压下ITO层中的光学变化。这项工作建立了我们对电可调等离子体材料的理解，并有助于设计超紧凑的活性纳米光子元件。

更新日期：2018-02-14

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