Infrared detector for smartphones and autonomous vehicles

Jülich, 17. August 2021

Jülich researchers, together with Italian and German colleagues, have developed a particularly inexpensive infrared detector that can be easily integrated into existing camera chips and smartphones. The new sensor makes two technically important ranges of infrared radiation visible. Those were previously not covered by conventional photodiodes. The results were presented in the journal ACS Photonics.

The world appears clearer in short-wave infrared, or SWIR for short: cameras operating in this range of the spectrum deliver images in grayscale - usually pin sharp. This is because such photochips can easily see through rain, fog or haze. Visible light is scattered by small water droplets in the air - which appears as a veil on the image, limiting visibility and detail capture. However, this effect does not play a role for light in the SWIR range. Therefore, such cameras are ideal for applications where a clear view is essential, for example for autonomous driving cars or aviation safety.

Image of San Francisco Bay in visible light (left) and shortwave infrared (right).

However, conventional camera chips made of silicon can only image the SWIR range to a very limited extent. "There are already other cameras that are used for these purposes. However, the very high costs often prevent their use in everyday life," explains Dan Buca from Forschungszentrum Jülich. The use of materials that are difficult to combine with standard silicon circuits makes integration into a chip complex and thus expensive: "Our detector therefore fills a gap: It covers a range of the spectrum for which no inexpensive sensors existed until now. The choice of alloys and elements that are well compatible with silicon now enables us to use comparatively simple manufacturing processes with standard tools. This allows us to design very low-cost camera chips that can be installed in any smartphone just as they are in today's cameras," adds Dan Buca.

The basis for the new detector is a thin layer of silicon, the standard material for computer chips. On top of this are deposited further layers of semiconductor materials containing the elements germanium and tin, all in the same main group in the periodic table as silicon.

"The germanium-tin semiconductors were developed in Jülich," explains Prof. Giovanni Isella of the Polytechnic of Milan, who led the development of the new device together with Dan Buca. "It took almost ten years to optimize all the parameters. But now these semiconductor layers can be built in any chip factory using established technology." This makes it possible to produce them particularly cheaply. And because they are based on silicon, they can also be integrated on existing chips without major problems.

The detector developed at Jülich makes hidden letters visible in the NIR and SWIR range (VIS = visible light/camera).
Forschungszentrum Jülich / Politecnico di Milano

For example, the various semiconductor layers can be used to produce pixels on photochips for digital cameras - which are then able to record the same images in different areas of the infrared spectrum. This allows some objects to appear in a different light, literally: "With paintings, for example, we can use it to look through layers of paint and see what the artist has painted underneath," says Giovanni Isella. Furthermore, certain printing inks used as security features for banknotes seem to disappear when viewed under IR light. The Jülich detector would therefore make it easy to check the authenticity of the banknotes.

Switcheable wavelengths

One special feature of the detector is that it is sensitive to two different ranges of the infrared spectrum. To do this, the bias voltage applied to it simply needs to be reversed - and the component switches from near infrared (NIR) to shortwave infrared (SWIR). "This allows us to expand the sensor's range of applications," says Giovanni Isella.

The liquids isopropanol and toluene appear transparent to the naked eye. Different proportions are absorbed in the NIR and SWIR ranges, which in combination allows accurate determination.
SImola et al., ACS Photonics 2021, 8, 7, 2166-2173 (CC BY-NC-ND 4.0)

In this way, it is possible, for example, to distinguish between different liquids and gases that absorb NIR and SWIR radiation to different degrees. The research team was able to demonstrate this using the solvents isopropanol and toluene as examples. With the aid of the switchable detector, the liquids, which are colorless to the human eye, can be clearly distinguished. This is not only useful for applications in the chemistry laboratory, but also interesting for a wide range of other everyday applications.

The results published in ACS Photonics are just the first step in unlocking the application potential of the NIR/SWIR double-band detector. The research teams involved are continuing their collaboration with the goal of developing a commercial product.

Original publication:

CMOS-Compatible Bias-Tunable Dual-Band Detector Based on GeSn/Ge/Si Coupled Photodiodes
Enrico Talamas Simola, Vivien Kiyek, Andrea Ballabio, Viktoria Schlykow, Jacopo Frigerio, Carlo Zucchetti, Andrea De Iacovo, Lorenzo Colace, Yuji Yamamoto, Giovanni Capellini, Detlev Grützmacher, Dan Buca and Giovanni Isella
ACS Photonics, 2021,8, 2166-2173, DOI: 10.1021/acsphotonics.1c00617

Further information:

High efficiency laser for silicon chips

Peter Grünberg Institute, Semiconductor Nanoelectronics (PGI-9)


Dr. Dan Mihai Buca
Forschungszentrum Jülich, Peter Grünberg Institute (PGI-9)
Tel: +49 2461 61-3663

Prof. Dr. Detlev Grützmacher
Leiter des Peter Grünberg Instituts (PGI-9), Forschungszentrum Jülich
Tel: +49 2461 61-2340

Press contact:

Tobias Schlößer
Forschungszentrum Jülich, Corporate Communications
Tel.: +49 2461 61-4771

Last Modified: 16.08.2022