July 18, 2024
Detection of Ultra-Broadband Photons 1

Improving the Detection of Ultra-Broadband Photons with a Twisted Double Bilayer Graphene Device

Researchers have made significant advancements in ultra-broadband photodetection with the development of a device based on twisted double bilayer graphene (TDBG). This breakthrough has the potential to revolutionize hyperspectral imaging, enabling applications in various fields such as autonomous driving, environmental monitoring, healthcare, space exploration, agriculture, and food processing.

Hyperspectral imaging, which utilizes the full spectrum of light, is crucial for gaining detailed insights into nature and its behavior. However, current technology faces challenges when it comes to imaging in the infrared to the terahertz regime. Existing devices, such as photoconductor arrays based on mercury cadmium telluride elements, are only partially effective, as they tend to be efficient absorbers for certain wavelengths but perform worse for others. Additionally, these devices are unable to detect the longest wavelengths of light in the terahertz regime.

To address these limitations, researchers have turned to twisted double bilayer graphene. Bilayer graphene (BLG) has already demonstrated impressive photodetection capabilities when biased with external electric fields. However, due to its 2D nature, BLG’s light absorption is relatively limited. Twisted double bilayer graphene (TDBG), on the other hand, offers a solution by creating its own intrinsic electric field without the need for additional electrodes.

In a study published in Nature Photonics, researchers from ICFO, ETH Zurich, the University of Manchester, NIMS in Japan, and CNRS in France report on the development of a TDBG ultra-broadband photodetector capable of detecting light efficiently across a broad spectral range. This spectral range spans from the far-terahertz to near-infrared wavelengths, with continuous efficiency throughout the range.

The TDBG device exhibits good internal quantum efficiency and enhanced photoconductivity through interlayer screening. Unlike previous devices, TDBG does not require the application of external electric fields, making it more scalable for industrial applications.

To test the light detection capabilities of TDBG, researchers conducted a comprehensive study of the device’s photoresponse. Multiple TDBG devices were fabricated and their photoconductivity, or changes in electrical resistance under illumination, was analyzed. The results were promising, showing a significant drop in resistance upon illumination by mid-infrared light. This suggests that TDBG devices can be utilized as efficient photodetectors.

The research team faced their fair share of challenges, including the complex fabrication process of TDBG samples. Obtaining large enough flakes of bilayer graphene, cutting them in half, and stacking them to create a TDBG stack required meticulous precision. The devices were then cooled to 4 Kelvin to perform precise measurements of electrical resistance.

Despite the challenges, the researchers persevered and managed to collect and understand the data, quantifying the device’s internal quantum efficiency. They found that the device’s efficiency was above 40% for most of the spectral range, a promising result when combined with TDBG’s ultra-broad spectral range and scalability.

Further measurements conducted in the lab of Giacomo Scalari in Switzerland demonstrated that the TDBG photodetector could operate in the long-wavelength range, extending down to 2 THz. The researchers also identified the photoconductive effect as the primary mechanism behind the device’s response, where photons create more electron-hole pairs directly, rather than influencing resistance through temperature changes.

The findings of this study provide a guide and benchmark for future research on twisted materials. The conductivity enhancement through interlayer screening, the differentiation between bolometric and photoconductive responses, and the proposed idea of 3-dimensional stacking could be applied to further research on other two-dimensional materials.

In conclusion, the development of the TDBG ultra-broadband photodetector represents a significant advancement in the field of hyperspectral imaging. With its ability to detect light efficiently across a wide spectral range, TDBG holds great potential for various applications in sectors such as automotive, healthcare, agriculture, and more.

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1.Source: Coherent Market Insights, Public sources, Desk research
2.We have leveraged AI tools to mine information and compile it