Manijeh Razeghi. Credit: Northwestern University
Night-vision cameras have revolutionized the security industry with their amazing ability to survey areas in complete darkness. The present night-vision cameras often fail as the materials and technology used in the cameras degrade under temperature stress.
A new approach in improving the technologies in night-vision cameras and avoiding frequent breakdowns has been developed by Northwestern Engineering’s Manijeh Razeghi and her team.
Razeghi’s team has developed a new design of strained-layer indium arsenide/indium arsenide antimonide type-II superlattices. The superlattices are key components used for making high-performance, long-wavelength infrared photodetectors for various applications, including night-vision cameras.
With a special superlattice-based electron barrier, the newly designed photodetector limits the obstructing dark current density, while raising the background limited infrared photodetection temperature. This enables the infrared cameras to perform imaging at higher operating temperatures and reduces the need for cryogenic cooling power inside the camera.
Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science in Northwestern’s McCormick School of Engineering
The team’s research, published earlier this month in the
APL Materials, was supported by the Air Force Research Laboratory, Defense Advanced Research Projects Agency, and US Army.
The wavelength of signals emitted by the human body is 10 microns, and the new photodetector developed by Razeghi can detect the light signals up to this value. Currently, the sophisticated photodetectors are made using mercury-cadmium-telluride, and since this compound degrades under thermal stress, scientists were in search for alternatives.
Additionally, the health and environmental dangers caused by mercury are well-known. (From 2020, the international Minamata Convention of Mercury will prohibit the production and trade of products with mercury.)
Razeghi’s group in Northwestern’s Center for Quantum Devices has pioneered the replacement of mercury with indium arsenide/indium arsenide antimonide type-II superlattices. The new replacement is safer and more durable than mercury. The heat-sensitive ionic bonds in mercury-cadmium-telluride degrade under high temperatures.
Earlier efforts to employ indium arsenide/indium arsenide antimonide type-II superlattices had resulted in photodetectors having inferior optical performance and shorter lifetimes. However, Razeghi and her team’s new “saw-tooth superlattice design” solved this long-lasting scientific challenge. The new design of superlattice acts as an electron barrier to protect the material, thus preventing degradation.