▎ 摘　　要

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. Optics: designing lightweight, broadband graphene photodetectorsAmerican scientists have developed graphene photodetectors with unprecedented compactness, ultra-broadband detection, and ultrafast response speeds. In addition to being inexpensive, lightweight, and compact, graphene has unique optical and electrical properties, including a zero bandgap, ultrahigh carrier mobility, and thermal conductance that make it ideal for use in photodetectors. However, as graphene is just one monolayer, it absorbs light very weakly, thus hindering the development of practical photodetectors. A team of researchers led by Vladimir Shalaev from Purdue University in the United States has developed a plasmonic-enhanced graphene photodetector with a 25-fold increase in photocurrent generation compared with conventional graphene devices. Moreover, further enhancement can be achieved by the application of a direct current bias, opening the door for useful applications that require small devices with broad operational bandwidths and excellent responsivity.