Microcavity-integrated graphene photodetector

Abstract: The monolithic integration of novel nanomaterials with mature and established technologies has considerably widened the scope and potential of nanophotonics. For example, the integration of single semiconductor quantum dots into photonic crystals has enabled highly efficient single-photon sources. Recently, there has also been an increasing interest in using graphene - a single atomic layer of carbon - for optoelectronic devices. However, being an inherently weak optical absorber (only 2.3 % absorption), graphene has to be incorporated into a high-performance optical resonator or waveguide to increase the absorption and take full advantage of its unique optical properties. Here, we demonstrate that by monolithically integrating graphene with a Fabry-Perot microcavity, the optical absorption is 26-fold enhanced, reaching values >60 %. We present a graphene-based microcavity photodetector with record responsivity of 21 mA/W. Our approach can be applied to a variety of other graphene devices, such as electro-absorption modulators, variable optical attenuators, or light emitters, and provides a new route to graphene photonics with the potential for applications in communications, security, sensing and spectroscopy.

• The paper presents the main contribution of achieving a 26-fold optical absorption enhancement, increasing graphene's absorption from about 2.3% to over 60% via microcavity integration.
• The methodology employs a sandwich design with distributed Bragg mirrors and transfer matrix simulation, leading to a record responsivity of 21 mA/W.
• The findings imply potential applications in advanced photonic devices, including communications and sensing, with enhanced spectral selectivity around 855 nm.

Integration of Graphene and Microcavity for Enhanced Photodetection

The paper presents an innovative approach to augmenting the optical absorption capabilities of graphene through integration with a Fabry-Pérot microcavity. This research showcases the substantial enhancement of graphene's optical absorption and responsivity when embedded within a microcavity structure, addressing the key limitation of graphene's inherently weak optical absorption (approximately 2.3%).

Key Findings

1. Optical Absorption Enhancement: By monolithically integrating graphene with a Fabry-Pérot microcavity, the researchers achieved a 26-fold enhancement in optical absorption, reaching over 60%. This is a significant improvement from standalone graphene, which absorbs merely about 2.3% of incident light.
2. Responsivity Achievements: The study demonstrates a graphene-based microcavity photodetector that achieved a record responsivity of 21 mA/W. This enhancement makes it the highest reported responsivity for graphene photodetectors to date.
3. Device Design: The device configuration involves a single to bi-layer graphene sheet sandwiched between distributed Bragg mirrors, which are composed of materials with large band gaps that are non-absorbing at the detection wavelength. This sandwich architecture is instrumental in trapping light within the cavity, significantly boosting the interaction with graphene.
4. Theoretical and Simulation Methods: The device performance was improved using the transfer matrix method to optimize the microcavity's optical properties. Simulation results closely matched experimental outcomes, indicating reliable predictive modeling.
5. Spectral Response: The photodetector exhibited a sharp spectral photocurrent response peaking at the cavity resonance (around 855 nm), with a 9 nm full width at half maximum. This selective response is promising for applications in wavelength division multiplexing (WDM).

Implications and Future Prospects

The successful enhancement of graphene's optoelectronic properties by embedding it into a resonant microcavity paves the way for potential applications beyond photodetection. The proposed method can also be applied to other graphene-based devices such as electro-absorption modulators, variable optical attenuators, and light emitters. These advancements have implications for fields such as telecommunications, security, and sensing technologies.

The research demonstrates the feasibility of monolithic integration of carbon nanomaterials with optical cavities, which could lead to the development of novel photonic devices combining the superior electrical properties of graphene with high optical efficiency. The findings also encourage further exploration of different cavity designs and material systems to optimize device performance across a wider range of wavelengths.

Conclusion

This study represents a significant contribution to the field of graphene photonics by demonstrating enhanced light absorption and responsivity through the strategic integration of microcavity structures. The approach not only provides a viable solution to the limitations posed by graphene's low optical absorption but also opens new avenues for advanced optoelectronic device designs. Future work could involve refining the fabrication process, exploring other material systems, and extending the research to practical applications in communication and sensing technologies.