[论文解读] Conductivity in organic semiconductors mediated by polaritonic states

Emanuele Orgiu, Jino George+8 more|arXiv (Cornell University)|Sep 5, 2014

Strong Light-Matter Interactions参考文献 14被引用 2

一句话总结

本文提出通过使用等离子体结构将有机半导体强烈耦合到真空电磁场，形成极化子态，使电荷载流子在约10^5个分子范围内离域化，从而增强电导率。在共振时，由于场效应迁移率相应提高，电流增加了一个数量级，该结果得到量子模型和晶体管测量的验证。

ABSTRACT

Organic semiconductors have generated considerable interest for their potential for creating inexpensive and flexible devices easily processed on a large scale [1-11]. However technological applications are currently limited by the low mobility of the charge carriers associated with the disorder in these materials [5-8]. Much effort over the past decades has therefore been focused on optimizing the organisation of the material or the devices to improve carrier mobility. Here we take a radically different path to solving this problem, namely by injecting carriers into states that are hybridized to the vacuum electromagnetic field. These are coherent states that can extend over as many as 10^5 molecules and should thereby favour conductivity in such materials. To test this idea, organic semiconductors were strongly coupled to the vacuum electromagnetic field on plasmonic structures to form polaritonic states with large Rabi splittings ca. 0.7 eV. Conductivity experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility as revealed when the structure is gated in a transistor configuration. A theoretical quantum model is presented that confirms the delocalization of the wave-functions of the hybridized states and the consequences on the conductivity. While this is a proof-of-principle study, in practice conductivity mediated by light-matter hybridized states is easy to implement and we therefore expect that it will be used to improve organic devices. More broadly our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.

研究动机与目标

• 为克服材料无序导致的有机半导体中电荷载流子迁移率低下的问题。
• 探索通过调控真空电磁环境来提升电导率的新方法。
• 检验杂化光-物质态（极化子）是否能增强载流子迁移率和电导率。
• 验证相干、离域态在提升器件性能中的作用。
• 展示一种无需结构优化即可提升有机半导体器件的可扩展方法。

提出的方法

• 利用等离子体纳米结构使有机半导体与真空电磁场实现强耦合。
• 系统实现了约0.7 eV的较大Rabi分裂，表明光与物质之间存在强相互作用。
• 在场效应晶体管结构中测量电导率，以分离迁移率变化的影响。
• 建立了理论量子模型，描述杂化态波函数的离域化行为。
• 调节共振条件以最大化耦合并测量电导率的增强。
• 在栅压控制下进行测量，以区分迁移率变化与其他效应的影响。

实验结果

研究问题

• RQ1 有机半导体与真空电磁场之间的强耦合是否能增强电荷载流子迁移率？
• RQ2 极化子态在有机半导体的分子聚集体中能离域多大范围？
• RQ3 杂化光-物质态的形成是否导致电导率的可测量提升？
• RQ4 在晶体管结构中，共振耦合下场效应迁移率如何变化？
• RQ5 调控真空电磁环境是否可作为提升有机半导体性能的通用策略？

主要发现

• 在强耦合态的共振条件下，电导率提高了整整一个数量级。
• 观察到的电流增强主要源于场效应迁移率的显著提升，而非载流子浓度的增加。
• 理论建模证实，杂化态中的波函数可在多达10^5个分子范围内实现离域化。
• 约0.7 eV的Rabi分裂证实了系统中存在强光-物质耦合。
• 该增强效应具有可逆性和可调性，通过栅压实现，证实其源于迁移率而非掺杂。
• 该方法提供了一种可扩展、非侵入性的有机半导体器件性能提升途径，无需改变材料结构。