Full view: "thermal vision" sensors will help technology see better through interference

An international team of researchers with the participation of Russian scientists has created a unique infrared sensor that is able to simultaneously "see" radiation in two ways — as a conventional photodetector and as a thermal sensor. The new technology will make it possible to more accurately detect objects and distinguish materials by their temperature trace, and in the future it may find application in thermal imagers, night vision systems, industrial diagnostics and space technology. The sensor is suitable for operation in conditions of optical interference, for example, in conditions of smoke, fog or dust, experts told Izvestia.

New dual-use sensors

Scientists have developed an infrared detector capable of detecting radiation simultaneously in two different ways.: as a classical photodetector and as a thermal sensor. The work was carried out by an international team, which included leading Russian researchers from MISIS, Moscow State University, RCC and the Higher School of Economics. The new approach opens up opportunities for creating highly efficient next-generation devices that will be able to analyze objects with different temperatures, better "see" through optical interference, and more accurately distinguish materials and objects by their thermal footprint.

Infrared detectors are used in industrial control, medicine, ecology, night vision systems and space technology, scientists told Izvestia. Typically, such devices operate according to one of two principles: either photovoltaic sensors directly convert photons into an electrical signal, or thermal sensors detect changes in the characteristics of materials due to heating under the influence of radiation.

To combine both of these principles, scientists have developed an innovative infrared sensor based on lead telluride single crystals, which for the first time combines two radiation detection mechanisms — photoelectric and thermal, thereby increasing the efficiency of object detection.

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"We have shown that a single semiconductor element is capable of detecting infrared radiation in two different physical ways. At the same time, the mechanisms practically do not affect each other. When exposed to medium-wavelength infrared radiation with a wavelength of 2-5 microns, the device works like a conventional photodiode. With longer wavelength radiation, from 10.6 microns, another mechanism is activated — the barrier pyroelectric effect," said Danil Kobtsev, a laboratory researcher at the Laboratory of Photonic gas sensors at NUST MISIS.

Lead telluride belongs to materials with a center of symmetry that are unable to exhibit a pyroelectric effect under normal conditions, the authors of the project said.

— We introduced an admixture of indium into it and formed a p–n junction (the area of contact between two semiconductors with different types of conductivity), due to which a built-in electric field appeared inside the crystal. It broke the local symmetry by shifting the sublattices of ions relative to each other. As a result, we have obtained a large electrical signal that can be used to detect radiation with an energy lower than the band gap. At the same time, the material retained all its standard photovoltaic characteristics, which made it possible to combine two IR detection mechanisms in one device," explained Vadim Kovalyuk, head of the Laboratory of Photonic Gas Sensors at NUST MISIS.

Highly sensitive thermal vision

The researchers confirmed the operability of the experimental samples in the typical temperature range for high—precision detectors - from -233 to -83 degrees. The tests showed high sensitivity in the photovoltaic mode, stable thermal response and stable performance during long-term operation.

—The proposed semiconductor architecture creates the basis for the development of universal, compact and precise matrix sensors that can be used in thermal imaging, surveillance systems, as well as for industrial diagnostics and scientific research," said Grigory Goltsman, Chief Researcher at the NTI MISIS Laboratory of Quantum Communications.

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The main advantage of such dual photodetectors over classical designs based on gallium arsenide, indium phosphide or indium antimonide is the extended range of light detection. By combining the two recognition methods, the spectral sensitivity range of the source material, lead telluride, is expanded. This determines the potential application of spectrometers, Dmitry Getz, Candidate of Physico—Mathematical Sciences, leading researcher at the New ITMO Physics and Technology Institute, told Izvestia.

"The use of the developed photodetectors in the creation of IR cameras is particularly promising," he said.

Such sensors are interesting primarily because the same device can operate in two modes at once.: as a photodetector and as a thermal sensor, noted Sergey Sazonov, NTI expert on microelectronics and the electronics industry. This means that it can be used to analyze objects with different temperatures, to more accurately distinguish materials by their thermal trace, and to work in conditions where there is optical interference, such as smoke, fog, and dust. This opens up several very practical areas for technology.

— The development of a new generation of thermal imagers and surveillance systems will be useful. Here, the dual mode will help you to see objects better in difficult conditions, distinguish between disguises and increase the reliability of detection. In medicine, such sensors can form the basis of more accurate non-contact thermometers and diagnostic systems. In the future, this will also include space technology, security systems and scientific instruments, where compactness, sensitivity and a wide range of work are important," the specialist said.

The details of the study are published in the Journal of Applied Physics. The project was implemented with the support of the Russian Science Foundation and the Ministry of Science and Higher Education.