Generation of photovoltage in graphene on a femtosecond time scale through efficient carrier heating (1504.06487v1)

Abstract: Graphene is a promising material for ultrafast and broadband photodetection. Earlier studies addressed the general operation of graphene-based photo-thermoelectric devices, and the switching speed, which is limited by the charge carrier cooling time, on the order of picoseconds. However, the generation of the photovoltage could occur at a much faster time scale, as it is associated with the carrier heating time. Here, we measure the photovoltage generation time and find it to be faster than 50 femtoseconds. As a proof-of-principle application of this ultrafast photodetector, we use graphene to directly measure, electrically, the pulse duration of a sub-50 femtosecond laser pulse. The observation that carrier heating is ultrafast suggests that energy from absorbed photons can be efficiently transferred to carrier heat. To study this, we examine the spectral response and find a constant spectral responsivity between 500 and 1500 nm. This is consistent with efficient electron heating. These results are promising for ultrafast femtosecond and broadband photodetector applications.

• The paper demonstrates that graphene generates photovoltage in under 50 fs via rapid carrier heating.
• It uses sub-50 fs time-resolved measurements to accurately map ultrafast electron dynamics.
• The study highlights graphene’s broadband spectral response, underscoring its potential for next-generation photodetectors.

Photovoltage Generation in Graphene on Femtosecond Time Scales

The paper explores the ultrafast dynamics of photovoltage generation in graphene and evaluates its potential for advanced photodetection applications. By leveraging the unique properties of graphene, this paper aims to characterize the photovoltage generation time and its implications for photodetector performance.

Key Findings and Methodology

Graphene's promise as a versatile photodetector arises from its broad spectral range capabilities and rapid response times. The research focuses on the photo-thermoelectric effect (PTE), where local electron heating leads to photovoltage generation. Utilizing time-resolved measurements, the paper establishes that the photovoltage generation occurs in less than 50 femtoseconds (fs), highlighting the efficiency of carrier heating in graphene.

1. Experimental Setup: The paper employs a time-resolved photovoltage measurement technique with sub-50 fs laser pulses, distinctly mapping the ultrafast electron dynamics in graphene. This setup involves ultrafast laser sources and sensitive detection, enabling precise monitoring of the heating and cooling stages of electron dynamics.
2. Carrier Heating and Photovoltage Generation: The crucial finding is that the carrier heating—and thus photovoltage generation—occurs significantly faster than conventional electron cooling processes. This rapid heating is facilitated by efficient carrier-carrier scattering mechanisms.
3. Broadband Spectral Responsivity: The spectral response of graphene photodetectors remains constant across a wide spectral range from 500 to 1500 nm, indicating high photon-to-electron heat conversion efficiency. This characteristic underscores graphene's potential for broadband photodetective applications.
4. Theoretical Models and Simulations: Theoretical models corroborate experimental observations, quantifying the efficiency of electron heating and its impact on photovoltage generation. These models aid in understanding the energy transfer dynamics between photoexcited carriers and the graphene lattice.

Implications for Future Photodetector Development

The high-speed carrier dynamics and broadband absorption properties make graphene a compelling candidate for advanced optoelectronic applications, particularly where ultrafast response times are paramount. Potential applications include ultrafast cameras, next-generation communications, and precise optical measurements.

• Technological Impact: Devices based on ultrafast and broadband characteristics of graphene could revolutionize the efficiency and capability of photodetectors in various technologies.
• Further Research Directions: Investigations could extend to hybrid systems combining graphene with other 2D materials to optimize performance parameters such as responsivity and efficiency further.

Conclusion

This paper emphasizes the advantageous properties of graphene that arise from its unique electron dynamics. The demonstrated femtosecond-scale photovoltage generation and consistent spectral responsivity position graphene as a promising material in the evolution of photodetector technologies. By expanding the understanding of graphene's fast heating dynamics, this paper sets the foundation for future advancements in optoelectronic applications.