Planar carbon nanotube-graphene hybrid films for high-performance broadband photodetectors

Abstract: Graphene has emerged as a promising material for photonic applications fuelled by its superior electronic and optical properties. However, the photoresponsivity is limited by the low absorption cross section and ultrafast recombination rates of photoexcited carriers. Here we demonstrate a photoconductive gain of $\sim$ 10$^5$ electrons per photon in a carbon nanotube-graphene one dimensional-two dimensional hybrid due to efficient photocarriers generation and transport within the nanostructure. A broadband photodetector (covering 400 nm to 1550 nm) based on such hybrid films is fabricated with a high photoresponsivity of more than 100 AW$^{-1}$ and a fast response time of approximately 100 {\mu}s. The combination of ultra-broad bandwidth, high responsivities and fast operating speeds affords new opportunities for facile and scalable fabrication of all-carbon optoelectronic devices.

• The paper demonstrates that integrating 1D SWNTs with 2D graphene in planar hybrid films significantly enhances photocarrier generation and transport.
• The paper reports a photoconductive gain of ~10 electrons per photon and responsivity over 100 A/W across a broadband spectrum from 400 nm to 1550 nm.
• The paper observes a fast 100 μs response time, underscoring the device's potential for high-speed optical communication and real-time sensing.

Planar Carbon Nanotube-Graphene Hybrid Films for High-Performance Broadband Photodetectors

This paper presents a study on the development of planar carbon nanotube-graphene hybrid films designed as high-performance broadband photodetectors. The work effectively confronts the limitations in graphene-based photodetectors, particularly low photoresponsivity due to minimal absorption and fast carrier recombination. By integrating one-dimensional single-walled carbon nanotubes (SWNTs) with two-dimensional graphene sheets, the study enhances photocarrier generation and transport, achieving significant improvements in photoconductive gain and responsivity.

The study details the synthesis of large-area SWNT-graphene hybrid films, marking the first implementation of these films in optoelectronic devices. The approach exploits the robust excitonic behavior inherent in one-dimensional systems and translates it into a 2D layered material environment, laying the groundwork for high-performance optoelectronic heterostructures.

Key Findings and Numerical Results

1. Photoconductive Gain: The hybrid photodetectors exhibit a photoconductive gain of approximately 10 electrons per photon, a notable figure reflecting the efficiency of photocarrier generation and transport.
2. Responsivity: The photodetectors achieved a high responsivity of over 100 A/W across a broadband range from 400 nm to 1550 nm. This level of responsivity surpasses that of conventional graphene photodetectors and aligns with the demands for broadband applications in telecommunications and spectroscopy.
3. Response Time: A rapid response time of approximately 100 μs was observed, indicating the device’s suitability for high-speed optical applications. This speed supports bandwidth capacities that surpass previous quantum-dot-graphene detectors, making it viable for real-time applications.
4. Spectral Coverage: The devices maintain high responsivity across visible to near-infrared spectra, representing a significant advancement in achieving ultra-broadband photodetection.

Implications and Future Directions

The findings demonstrate that carbon nanotube-graphene hybrid films can serve as scalable and efficient components for optoelectronic devices, opening pathways for applications in optical communication, remote sensing, spectroscopy, and imaging. The integration of 1D SWNTs with 2D graphene not only enhances photodetector performance but also suggests broader strategies for improving optoelectronic devices by exploiting hybrid material structures.

Future research could focus on further optimization strategies, such as refining the alignment and density of SWNTs within the hybrid films, as well as exploring the impact of different tube chiralities and diameters on the device performance. Additionally, investigating the interactions at the nanoscale between these hybrid materials could provide insights into novel electronic properties and potential new applications in various nanotechnology domains.

In conclusion, the development of planar SWNT-graphene hybrid films represents a significant achievement, providing a potent combination of high responsivity, fast response times, and wide spectral coverage that enhances the capability of broadband photodetectors for diverse applications. This research enriches the understanding and utility of carbon-based hybrid materials in advanced nanodevices, indicating notable practical and theoretical advancements in the field of optoelectronics.