Metallic nanostructures can be used to selectively absorb a specific regime of the infrared (IR) spectrum depending on its constituent materials and geometry. In this paper, we propose and analyze a plasmo-thermomechanical detector that includes a graphene layer on top of metallic nanowires to enhance the absorption and sensitivity. The proposed device converts the free-space IR radiation to mechanical deformation of nanowires that modulates the insertion loss of the waveguide underneath the nanowires and facilitates the on-chip optical readout of the free-space radiation at room temperature. Our design takes advantage of localized surface plasmon resonances to maximize absorption at the desired IR spectrum. We provide a systematic investigation of different material combinations with and without graphene in addition to variations in detector geometry to optimize the designed IR detector. On top of the absorption enhancement, the graphene layer over the nanowires boosts thermal relaxation speed of the nanowires by 3 times due to graphene’s high thermal conductivity, in turn speeding up the response of the IR detection. Moreover, the coated graphene layer enhances the mechanical deformation by a factor of 6 and bends the suspended nanowires downward, enhancing the light–matter interaction between the nanowires and the waveguide evanescent field. Overall, incorporating graphene is beneficial for enhanced spectrum absorption, speed of the IR detection, and optical readout sensitivity.
Enhancing the graphene photocurrent using surface plasmons and a p-n junction
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.
more » « less- Award ID(s):
- 1641101
- NSF-PAR ID:
- 10173266
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Light: Science & Applications
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2047-7538
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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