Non-toxic materials open door for better cameras for consumer electronics

Shortwave infrared (SWIR) light is invisible to our eyes, but it can potentially revolutionize various industries, from robotics and automotive to consumer electronics. This is because light can penetrate fog, haze, and smoke, and it can also be used to detect certain materials that are invisible to visible light. One that makes SWIR more accessible is colloidal quantum dots (CQDs).

CQDs are tiny semiconductor particles that can be tuned to emit or absorb light of different wavelengths. This makes them ideal for use in SWIR sensors and imagers. However, there is one major roadblock to using CQDs in mass-market applications: many of them contain heavy metals like lead or mercury.

These metals are toxic and subject to strict regulations, making them difficult and expensive. In a recent study published in , researchers from ICFO and Qurv have reported a breakthrough in the development of SWIR CQDs. They have developed a new method for synthesizing size-tunable, phosphine-free silver telluride (Ag2Te) quantum dots.

These quantum dots are non-toxic and have excellent optical properties, making them ideal for use in SWIR sensors and imagers. The new method for synthesizing Ag2Te quantum dots is based on a novel precursor complex that does not contain phosphine. Phosphine is a highly toxic gas commonly used in the synthesis of CQDs, but it can also have a detrimental impact on the optical properties of the quantum dots.

By eliminating phosphine from the synthesis process, the researchers produced Ag2Te quantum dots with high quality and performance. The researchers then used the new Ag2Te quantum dots to fabricate a SWIR photodetector. The photodetector exhibited excellent performance, with a spectral range from 350nm to 1,600nm, a linear dynamic range exceeding 118 dB, and a room temperature detectivity of the order 1012 Jones.

To the best of our knowledge, the photodiodes reported here have for the first time realized solution-processed, non-toxic shortwave infrared photodiodes with figures of merit on par with other heavy-metal containing counterparts,” said Gerasimos Konstantatos, ICREA Prof. at ICFO and leading author of the study. “These results further support the fact that Ag2Te quantum dots emerge as a promising RoHS-compliant material for low-cost, high-performance SWIR photodetectors applications.

” With the successful development of this heavy-metal-free quantum dot-based photodetector, the researchers went further. They teamed up with Qurv, an ICFO spin-off, to demonstrate its potential by constructing a SWIR image sensor as a case study. The team integrated the new photodiode with a CMOS-based read-out integrated circuit (ROIC) focal plane array (FPA), demonstrating a proof-of-concept, non-toxic, room temperature-operating SWIR quantum dot-based image sensor for the first time.

The authors of the study tested the imager to prove its operation in the SWIR by taking several pictures of a target object. In particular, they were able to image the transmission of silicon wafers under the SWIR light and to visualize the opaque content of plastic bottles in the visible light range. “Accessing the SWIR with a low-cost technology for consumer electronics will unleash the potential of this spectral range with a huge range of applications, including improved vision systems for the automotive industry (cars), enabling vision and driving under adverse weather conditions,” says Gerasimos Konstantatos.

“SWIR band around 1. 35–1. 40 µm, can provide an eye-safe window, free of background light under day/night conditions, thus, further enabling long-range light detection and ranging (LiDAR), three-dimensional imaging for automotive, augmented reality and virtual reality applications.

” The development of non-toxic, high-performance SWIR CQDs is a breakthrough that can potentially revolutionize a wide range of industries. These quantum dots could be used to develop new SWIR sensors and imagers for a variety of applications, including automotive, robotics, consumer electronics, and medical imaging. Study abstract: Photodetectors that are sensitive in the shortwave-infrared (SWIR) range (1–2 µm) are of great interest for applications such as machine vision, autonomous driving and three-dimensional, night and adverse weather imaging, among others.

Currently available technologies in the SWIR range rely on costly epitaxial semiconductors that are not monolithically integrated with complementary metal–oxide–semiconductor electronics. Solution-processed quantum dots can address this challenge by enabling low-cost manufacturing and simple monolithic integration on silicon in a back-end-of-line process. So far, colloidal quantum dot materials to access the SWIR regime are mostly based on lead sulfide and mercury telluride compounds, imposing major regulatory concerns for their deployment in consumer electronics due to the presence of toxic heavy metals.

Here we report a new synthesis method for environmentally friendly silver telluride quantum dots and their application in high-performance SWIR photodetectors. The colloidal quantum dot photodetector stack employs materials compliant with the Restriction of Hazardous Substances directives and is sensitive in the spectral range from 350 nm to 1,600 nm. The room-temperature detectivity is of the order of 1012 Jones, the 3 dB bandwidth is in excess of 0.

1 MHz and the linear dynamic range is over 118 dB. We also realize a monolithically integrated SWIR imager based on solution-processed, toxic-heavy-metal-free materials, thus paving the way for this technology to the consumer electronics market. .