Li Lingfei, Liu Wei, Gao Anyuan, Zhao Yaolong, Lu Qin, Yu Li, Wang Junzhuan, Yu Linwei, Shao Lei, Miao Feng, Shi Yi, Xu Yang, Wang Xiaomu
Department of Information Science & Electronic Engineering , Zhejiang University , Hangzhou 310058 , China.
Department of Physics , The Chinese University of Hong Kong , Shatin , Hong Kong SAR China.
Nano Lett. 2019 May 8;19(5):3295-3304. doi: 10.1021/acs.nanolett.9b00908. Epub 2019 Apr 26.
Photogenerated nonequilibrium hot carriers play a key role in graphene's intriguing optoelectronic properties. Compared to conventional photoexcitation, plasmon excitation can be engineered to enhance and control the generation and dynamics of hot carriers. Here, we report an unusual negative differential photoresponse of plasmon-induced "ultrahot" electrons in a graphene-boron nitride-graphene tunneling junction. We demonstrate nanocrescent gold plasmonic nanostructures that substantially enhance the absorption of long-wavelength photons whose energy is greatly below the tunneling barrier and significantly boost the electron thermalization in graphene. We further analyze the generation and transfer of ultrahot electrons under different bias and power conditions. We find that the competition among thermionic emission, the carrier-cooling effect, and the field effect results in a hitherto unusual negative differential photoresponse in the photocurrent-bias plot. Our results not only exemplify a promising platform for detecting low-energy photons, enhancing the photoresponse, and reducing the dark current but also reveal the critically coupled pathways for harvesting ultrahot carriers.
光生非平衡热载流子在石墨烯引人入胜的光电特性中起着关键作用。与传统光激发相比，等离激元激发可通过设计来增强和控制热载流子的产生及动力学。在此，我们报道了石墨烯-氮化硼-石墨烯隧道结中等离激元诱导的“超热”电子的一种异常负微分光响应。我们展示了纳米月牙形金等离激元纳米结构，其能大幅增强能量远低于隧道势垒的长波长光子的吸收，并显著提高石墨烯中的电子热化。我们进一步分析了不同偏置和功率条件下超热电子的产生和转移。我们发现，热电子发射、载流子冷却效应和场效应之间的竞争导致了光电流-偏置图中迄今为止异常的负微分光响应。我们的结果不仅例证了一个用于检测低能光子、增强光响应和降低暗电流的有前景的平台，还揭示了收集超热载流子的关键耦合路径。
