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Army Research Lab, Stony Brook Develop Nighttime Imaging Material

Photonics.com
Feb 2018
ADELPHI, Md., Feb. 16, 2018 — The U.S. Army Research Laboratory (ARL) and New York’s Stony Brook University have developed a new synthesis process for low-cost fabrication of a material previously discounted in literature for high-sensitivity IR cameras, opening new possibilities for future military nighttime operations.

The Molecular Beam Epitaxy (MBE) is being used by Army researchers to produce new infrared detector materials based on InAsSb. This is a III-V semiconductor, a class of materials also used in opto-electronics in many commercial products such as DVD players and cell phones.
The Molecular Beam Epitaxy (MBE) is being used by Army researchers to produce new infrared detector materials based on InAsSb. This is a III-V semiconductor, a class of materials also used in optoelectronics in many commercial products such as DVD players and cellphones. Courtesy of U.S. Army.

ARL's Wendy Sarney and Stefan Svensson led a novel approach to using the semiconductor indium arsenide antimonide (InAsSb), a material that has not been used before in high-performance IR cameras for long wavelengths. The best materials for the IR camera light-sensors are currently based on mercury cadmium telluride (HgCdTe), which belongs to the family of II-VI compounds.

"Unfortunately, they are very expensive, mostly because there are only military customers for this material," Svensson said.

InAsSb is a III-V semiconductor, which is a class of materials used in optoelectronics in many commercial products such as DVD players and cellphones.

"By using cameras that can see the faint IR light, soldiers can operate during night times," Sarney said. "The more sensitive such a camera is, or in other words, the smaller the color or temperature differences are that it can see, the more details that can be discerned on a battlefield and enemies can be detected at longer ranges. High-performance IR cameras are therefore extremely important for the Army."

The key in this discovery was the realization that the material needed to be undistorted by strain in order to see at 10 µm. This was a major difficulty that had to be overcome before InAsSb could be used as a sensor material. The performance of devices based on semiconductor materials also depends on the material's crystalline perfection. InAsSb has to be deposited onto a starting crystalline material (a substrate) which has a smaller spacing between the atoms. This size mismatch at the atomic scale must be managed extremely well in order for the light-sensitive material to work properly.

Among possible substrates, larger and cheaper ones typically have progressively smaller atomic spacing. Over several years ARL and Stony Brook found a way to manage the atomic spacing mismatch culminating in the current work which uses GaAs as a substrate, which is inexpensive and available in large sizes. Large-area substrates allow manufacturing of multiple camera sensors at the same time for commercial foundries.

ARL and Stony Brook combined strain-mediating techniques to effectively manage the 10 percent atomic spacing mismatch between the InAsSb sensing material and GaAs substrate. To do this, they deposited an intermediate layer of GaSb onto GaAs in a way that trapped most of the defects caused by the size mismatch. They then further increased the atomic spacing with a graded layer that also kept defects away from the InAsSb sensor material.

The material was examined with high-resolution transmission electron microscopy in order to make sure it had sufficient structural quality. They also found that the optical quality related to detection properties was remarkably high. This research shows a path to a practical, lower cost solution for the eventual fielding of night-vision systems based on III-V long wavelength IR materials.

ARL is part of the U.S. Army Research, Development and Engineering Command, which aims to provide innovative research, development and engineering for the Army.

BusinessU.S. Army Research LaboratorydefenseStony Brook UniversitymaterialsimagingAmericas

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