Quantum Dot SWIR Materials

August 5, 2025

We have previously introduced QD-CMOS technology, discussed applications and compared aspects of different SWIR sensing technologies. This post aims to introduce the most common commercial colloidal quantum dot (CQD) SWIR sensing materials. We will discuss important materials parameters, quality features and highlight Nanoco’s unique capabilities in this area. All materials are narrow bandgap semiconductors, enabling the ability to shift the first absorption peak from the NIR for small nanocrystals to the far end of the SWIR, with some materials even reaching the MWIR (>3 µm).

Lead sulphide (PbS) has been the dominant material in this field due to a combination of its narrow bandgap and available precursor chemistry, facilitating growth of high quality nanocrystals. Prior to commercial development, the material was studied for two decades in academia with early reports of PbS photodetectors dating back to 2005.[1] Today, PbS CQDs can be found in a range of commercial image sensor and camera products with spectral ranges covering up to 2000 nm, while further expansion of the spectral range up to 2500 nm is expected soon.

HEATWAVE® PbS CQDs – absorption spectra and TEM images, displaying highly uniform ensembles of nanocrystals

At Nanoco, PbS CQDs have reached full commercial maturity, producing nanocrystals of very high uniformity at commercial scale. Uniformity is a critical parameter for image sensor applications, as uniform nanocrystals pack into denser films with improved absorption properties. Further, good nanocrystal uniformity reduces the number of energy barriers that can hinder efficient charge transport and provides a more controlled environment for effective chemical passivation of surface defects – at least as important for good charge transport. Such defects arise from under-coordinated atoms on the surface of the nanocrystals, which due to the high surface-to-volume ratio, are a major culprit for poor device performance. Effectively controlling these key parameters enables the fabrication of high performance SWIR sensors.

While PbS is currently the most mature system, several other materials are in development for SWIR sensing applications, including mercury telluride (HgTe), silver telluride (Ag₂Te), as well as the III-V materials indium arsenide (InAs) and indium antimonide (InSb). In the EU, the RoHS Directive restricts the use of certain hazardous substances, including lead and mercury, in electronic and electrical equipment. At Nanoco, we have focussed on the development of RoHS-compliant III-V materials due to their unique combination of very high electron mobilities, low permittivity, along with their more covalent nature. Translating these characteristics to device properties, these materials promise SWIR sensors with nanosecond response times, as well as improved temperature stability, thus giving access to a broader range of applications and markets.

To progress lead-free device performance, we have developed unique synthesis methods based on Nanoco’s proprietary molecular seeding technology for the fabrication of high quality InAs and InSb CQDs.[2] InAs is the more mature system today, where we have achieved uniform nanocrystal growth up to 1800 nm, covering key commercial wavelengths. For InSb, we have achieved breakthrough results seeing well defined first absorption peaks well beyond 1400 nm – indicative of uniform size distributions. Given the material’s narrow bandgap, we further see opportunities to target longer wavelengths up to 3000 nm, offering a unique materials solution for this spectral range, free of regulated heavy metals.

HEATWAVE® InAs (top) and InSb (bottom) CQDs – absorption spectra and TEM images, displaying highly uniform ensembles of nanocrystals

Nanoco is a leading provider of electronic-grade CQD SWIR materials, with our high-quality HEATWAVE® nanoparticle portfolio ready for seamless integration into semiconductor fabrication environments. Backed by deep expertise spanning early-stage materials development through to scale-up and commercial production, we deliver support across the full materials lifecycle. Our commitment to excellence is reflected in our ISO 9001 and 14001 certifications, ensuring the highest quality standards throughout. We’re excited about the future of this technology and, together with our valued partners, are working to expand its reach across a wide range of applications and markets. Interested in CQD SWIR sensing technology? Get in touch with us or connect at one of our upcoming events this autumn.

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