Reviewed by Danielle Ellis, B.Sc.Sep 2 2024
Researchers at the Beijing Institute of Technology, China, under the direction of Professor Dr. Menglu Chen from the School of Optics and Photonics, have created VLWIR and LWIR photodetectors using semimetal HgTe CQDs. This research was published in the journal Light Science & Applications.
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The use of infrared spectra range matching with atmospheric windows in remote sensing, environmental monitoring, and weather forecasting has sparked widespread scientific interest. The Rayleigh scattering law states that the fourth power of the wavelength is inversely proportional to scattering.
This suggests that there are advantages in terms of propagation distance for both long-wave infrared (LWIR, 6-15 μm) and very long-wave infrared (VLWIR, 15-30 μm). Presently, costly bulk epitaxial materials constitute the foundation of commercial LWIR or VLWIR detectors, which necessitate a difficult flip-bonding procedure to couple with the read-out circuit.
CQDs are a novel kind of semiconductor that can process solutions in large quantities. Significant advancements in CQD infrared photodetection have been made in recent decades, including spectrometers, bio-imaging, hyperspectral imagers, and infrared cameras. While CQD's absorption spectra already span a variety of spectral ranges
While CQD absorption spectra now span several spectral ranges, from terahertz to near-infrared, relatively few CQD devices can reach LWIR. It is yet unknown if quantum dot photodetectors can penetrate the VLWIR area.
According to quantum confinement, the band gap of the corresponding molecule determines the CQD spectral range. Using the re-growth approach, they were able to create large-sized HgTe CQDs that remained stable for several months in a polar solution. This gives ligands a good exchange platform.
Additionally, surface passivation is developed to lessen mercury emission, and surface ionic modification is developed to provide exact doping. Due to the increased carrier mobility, the carrier transport efficiency is increased by a factor of 100. The photoresponse experiment and thin-film transistor demonstrate how the quantum efficiency of the device was restricted by the ratio of the electron channel length to the carrier drift length.
The 18 μm VLWIR and 10 μm LWIR CQD photodetectors benefit from treatments, which increase their specific detectivity and responsivity by a factor of 100.
“The proper ligands modification to achieve high mobility and decent carrier lifetime is vital for long wavelength photodetection. This work not only expands the photodetection wavelength on CQD but also motivates interest in bottom-up infrared photodetection beyond costly epitaxial growth semiconductor bulk,” the scientists added.
The Westlake Institute for Optoelectronics, the National Natural Science Foundation of China, Beijing National Laboratory for Condensed Matter Physics, funded this study.
Journal Reference:
Xue, X., et al. (2024) Very long wave infrared quantum dot photodetector up to 18 μm. Light Science & Applications. doi.org/10.1038/s41377-024-01436-y.