SWIR Sensing Technologies

June 24, 2025

As part of our blog series on short wave infrared (SWIR) sensing, we first established the general concepts and subsequently provided an overview of various applications in this wavelength range (1000 – 3000 nm).[1,2] In this article, we will take a look at the range of SWIR sensing technologies and compare the most established InGaAs with a variety of emerging technologies, such as Ge-Si and of course quantum dots. We will highlight underlying strengths and weaknesses of each technology, and considering manufacturing and economic factors, briefly explore technology fit for a range of different applications. SWIR sensing has been a niche segment within the overall image sensor market, dominated by major players such as Sony, SemiConductor Devices (SCD), and Hamamatsu, along with several smaller, vertically integrated companies developing their own sensors and cameras. Due to the absorption limit of silicon at 1100 nm, all SWIR sensors are based on the concept of combining silicon CMOS readout integrated circuits (ROICs) with SWIR sensitive small bandgap semiconductor materials. The most established system is based on thin layers of InGaAs, a small bandgap (0.75 eV) semiconductor which in its standard composition In0.53Ga0.47As is lattice matched to the InP substrate material it is grown on. The standard composition of InGaAs covers a spectral range up to 1700 nm and offers excellent performance with minimal defects in the lattice matched InGaAs layer. While this approach yields sensors with minimal noise and record high sensitivity, fabrication of the InGaAs focal plane array is a complex and costly process requiring the use of expensive InP substrates.

Technology Table

*Results reported for a sensor with peak sensitivity at 1400 nm

To tackle the challenges with InGaAs manufacturing, alternative low bandgap semiconductors have been explored. Another approach has been established by growing a SWIR sensitive layer of germanium (direct bandgap of 0.8 eV) on a silicon substrate (Ge-Si), thus negating the need for costly InP substrates. While this approach lowers the manufacturing costs drastically, meeting the performance of InGaAs technology has proved to be difficult. One major obstacle for this technology is the reduction of dark currents (noise), which emerges due to defects in the semiconductor as a result of imperfect lattice match at the silicon-germanium interface. Further to that, the spectral range of the technology is limited to 1650 nm.

Colloidal quantum dot (CQD) technology combines some of the advantages of the previous two technologies. Due to the inherent scalability of solution processing methods, manufacturing costs can be reduced at least by an order of magnitude compared to InGaAs. The absence of substrate-based semiconductor growth and required lattice matching also means that CQD technology gives access to the full range of low bandgap semiconductor materials, thus expanding spectral ranges up to 3000 nm and beyond. While the full range of CQD materials systems for SWIR sensing will be covered in more detail in a following article, the most common materials today are PbS and InAs, both offering spectral ranges well beyond 2000 nm in theory. In practice, the maximum spectral range of CQD materials depend on fundamental material’s characteristics, including the bulk bandgap, as well as more practical considerations like the ability to grow uniform nanocrystals to the required size.

CQD sensor fabrication is based on the deposition of a CQD layer on top of a Si CMOS ROIC, either in photoconductive mode or as part of a photodiode stack. Currently, the best devices have been demonstrated using PbS CQDs, due to the material’s extensive history of development. In 2021, STMicroelectronics reported a CQD global shutter sensor at 1400 nm with peak external quantum efficiencies of 60% and dark currents of less than 2.5 nA/mm2 (2V, 60 °C).[5] Furthermore, these results were reported on a wafer level platform with a 1.62 µm pixel size, highlighting the potential of this technology for mass manufacturing and device miniaturisation. While sensor performance data has clearly demonstrated the potential of CQD SWIR sensing, the technology still requires optimisation particularly for applications demanding higher resilience to elevated temperatures.

To address this, Nanoco is developing the next generation of materials (III-V CQDs) with the goal to meet the high performance benchmarks of PbS CQD devices and improve the stability. The rising interest in III-V materials was recently confirmed by Sony publishing their first results on the development of InAs CQD SWIR sensors with a spectral range covering close to 1600 nm (peak at 1450 nm).[6] The paper demonstrated a clear path forward for these devices and showed wafer level processing with high uniformity, highlighting the technology’s advantage in low cost and high volume manufacturing. This combination of performance and low cost will drive technology adoption in a set of new markets, ranging from consumer electronics to automotive, where SWIR sensing offers key advantages over visible and NIR sensing – as discussed in previous posts.[2] While CQD SWIR technology is unlikely to replace InGaAs in high end applications in machine vision, defence and space, it is poised for the development of a variety of new use cases in established and new markets, where high costs of InGaAs technology have previously been prohibitive. As outlined above, our next post will zoom in on CQD sensing technology and discuss aspects of the materials and properties that are important for SWIR sensing applications. If you have any questions about our capabilities and technology, as always, feel free to reach out.

References:

  1. https://www.nanocotechnologies.com/colloidal-quantum-dot-swir-image-sensing/
  2. https://www.nanocotechnologies.com/introducing-swir-sensing-applications/
  3. InGaAs: S. Manda et al., “High-definition Visible-SWIR InGaAs Image Sensor using Cu-Cu Bonding of III-V to Silicon Wafer,” 2019 IEEE International Electron Devices Meeting (IEDM), San Francisco, CA, USA, 2019, pp. 16.7.1-16.7.4, doi: 10.1109/IEDM19573.2019.8993432
  4. TriEye Raven product sheet: https://trieye.tech/raven/         
  5. STMicro Paper: J. S. Steckel et al., “1.62μm Global Shutter Quantum Dot Image Sensor Optimized for Near and Shortwave Infrared,” 2021 IEEE International Electron Devices Meeting (IEDM), San Francisco, CA, USA, 2021, pp. 23.4.1-23.4.4, doi: 10.1109/IEDM19574.2021.9720560
  6. O. Enoki et al., “Pb-Free Colloidal InAs Quantum Dot Image Sensor for Infrared,” 2024 IEEE International Electron Devices Meeting (IEDM), San Francisco, CA, USA, 2024, pp. 1-4, doi: 10.1109/IEDM50854.2024.10873373

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