TCAD software used to show feasibility of SWIR SPAD

Technology News |
By Ally Winning

Iris Switzerland plans to use the software to prove the fabrication feasibility of a short-wave infrared (SWIR) SPAD that it is developing for use in autonomous driving applications.

The startup, founded in 2017, develops and builds mid- and long-range SWIR detectors and flash LiDARs that are primarily used in autonomous driving applications.

The company’s device concept is based on an avalanche photodiode structure with a germanium-tin (GeSn) absorption layer for SWIR detection that shows a high peak responsivity.

Layout of GeSn single-photon avalanche diode (SPAD). Source: IRIS Switzerland SA

In the device, germanium-tin alloy is the absorption material and silicon is the multiplier material. TCAD simulations were performed with different doping and thicknesses of layers to extract an optimized electric field profile. The simulations help understand thermoelectric cooling requirements early in the SPAD development to achieve an optimized Peltier cooling system in the first fabricated photodiode.

The use of highly sensitive GeSn alloys instead of InGaAs or HgCdTe (mercury, cadmium telluride – MCT) allows for operation at optical wavelengths above 1.4-micron which are retina safe. They also allows an efficient covering of multiple wavelengths in the SWIR spectrum. Multi-spectral functionality in the SWIR provides enhanced situational awareness and viewing during adverse environmental conditions and helps generate a higher resolution image of a scene.

The principal application is ADAS where Iris Switzerland claims it can enhance autonomous driving in adverse climatic situations or light exposition. However, the technology is also suitable for the detection of gases, explosives and drugs. It can also be used to detect hydroxyl bearing minerals, sulfates, and carbonate materials produced naturally on earth – and human activities such as the burning of fossil fuels and deforestation – through SWIR spectroscopy.

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