Wang Di, Allcca Andres E Llacsahuanga, Chung Ting-Fung, Kildishev Alexander V, Chen Yong P, Boltasseva Alexandra, Shalaev Vladimir M
School of Electrical and Computer Engineering, Purdue University, West Lafayette IN, 47907 USA.
Birck Nanotechnology Center, Purdue University, West Lafayette IN, 47907 USA.
Light Sci Appl. 2020 Jul 20;9:126. doi: 10.1038/s41377-020-00344-1. eCollection 2020.
The recently proposed concept of graphene photodetectors offers remarkable properties such as unprecedented compactness, ultrabroadband detection, and an ultrafast response speed. However, owing to the low optical absorption of pristine monolayer graphene, the intrinsically low responsivity of graphene photodetectors significantly hinders the development of practical devices. To address this issue, numerous efforts have thus far been made to enhance the light-graphene interaction using plasmonic structures. These approaches, however, can be significantly advanced by leveraging the other critical aspect of graphene photoresponsivity enhancement-electrical junction control. It has been reported that the dominant photocarrier generation mechanism in graphene is the photothermoelectric (PTE) effect. Thus, the two energy conversion mechanisms involved in the graphene photodetection process are light-to-heat and heat-to-electricity conversions. In this work, we propose a meticulously designed device architecture to simultaneously enhance the two conversion efficiencies. Specifically, a gap plasmon structure is used to absorb a major portion of the incident light to induce localized heating, and a pair of split gates is used to produce a p-n junction in graphene to augment the PTE current generation. The gap plasmon structure and the split gates are designed to share common key components so that the proposed device architecture concurrently realizes both optical and electrical enhancements. We experimentally demonstrate the dominance of the PTE effect in graphene photocurrent generation and observe a 25-fold increase in the generated photocurrent compared to the un-enhanced cases. While further photocurrent enhancement can be achieved by applying a DC bias, the proposed device concept shows vast potential for practical applications.
最近提出的石墨烯光电探测器概念具有诸多卓越特性，如前所未有的紧凑性、超宽带探测以及超快响应速度。然而，由于原始单层石墨烯的光吸收较低，石墨烯光电探测器固有的低响应度严重阻碍了实际器件的发展。为解决这一问题，迄今为止人们已做出诸多努力，利用等离子体结构来增强光与石墨烯的相互作用。然而，通过利用石墨烯光响应增强的另一个关键方面——电结控制，这些方法可以得到显著改进。据报道，石墨烯中主要的光载流子产生机制是光热电（PTE）效应。因此，石墨烯光电探测过程中涉及的两种能量转换机制是光到热和热到电的转换。在这项工作中，我们提出一种精心设计的器件架构，以同时提高这两种转换效率。具体而言，间隙等离子体结构用于吸收大部分入射光以诱导局部加热，一对分裂栅用于在石墨烯中产生一个 p-n 结以增强 PTE 电流的产生。间隙等离子体结构和分裂栅被设计为共享共同的关键组件，从而使所提出的器件架构同时实现光学和电学增强。我们通过实验证明了 PTE 效应在石墨烯光电流产生中的主导地位，并观察到与未增强情况相比，产生的光电流增加了 25 倍。虽然通过施加直流偏置可以进一步提高光电流，但所提出的器件概念在实际应用中显示出巨大潜力。
