Etched thin films could dramatically cut cost of infrared detectors

Optical technology from an Australian collaboration of researchers could make infrared technology easy to use and cheap.

By etching grooves in the thin film of an infrared detector, the light is redirected and almost all of it is absorbed. The absorbing layer is less than 1/2000th the thickness of a human hair. (Image credit: Thomas P. White, Australian National University)
By etching grooves in the thin film of an infrared detector, the light is redirected and almost all of it is absorbed. The absorbing layer is less than 1/2000th the thickness of a human hair. (Image credit: Thomas P. White, Australian National University)

IMAGE: By etching grooves in the thin film of an infrared detector, the light is redirected and almost all of it is absorbed. The absorbing layer is less than 1/2000th the thickness of a human hair. (Image credit: Thomas P. White, Australian National University)

Research published in Optica details a breakthrough by an Australian collaboration of researchers that could make infrared technology easy to use and cheap, potentially saving millions of dollars in defense and other areas using sensing devices, and boosting applications of technology to a host of new areas, such as agriculture.

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Infrared (IR) devices are used for improved vision through fog and for night vision and for observations not possible with visible light; high-quality IR detectors cost approximately $100,000 (including the device at the University of Sydney) and some require cooling to -200°C. Now, research spearheaded by researchers at the University of Sydney (Sydney, Australia) has demonstrated a dramatic increase in the absorption efficiency of light in a layer of semiconductor that is only a few hundred atoms thick--to almost 99% light absorption from the current inefficient 7.7%.

Co-author from the University of Sydney's School of Physics, professor Martijn de Sterke, said the team discovered perfect thin film light absorbers could be created simply by etching grooves into them. "Conventional absorbers add bulk and cost to the infrared detector as well as the need for continuous power to keep the temperature down. The ultrathin absorbers can reduce these drawbacks," said de Sterke.

Co-lead author Björn Sturmberg, who carried out the research as a PhD student at the University of Sydney with the support of the Australian Renewable Energy Agency, said the findings did not rely upon a particular material but could be applied to many naturally occurring weak absorbers. "There are many applications that could greatly benefit from perfectly absorbing ultra-thin films, ranging from defence and autonomous farming robots to medical tools and consumer electronics," Sturmberg said.

The director of Australia's National Computational Infrastructure (NCI) and co-author, of the paper, professor Lindsay Botten, said the structures were much simpler to design and fabricate than using existing thin film light absorbers, that required either complex nanostructures, metamaterials and exotic materials, or difficult-to-create combinations of metals and non-metals. "There are major efficiency and sensitivity gains to be obtained from making photo-detectors with less material," he said.

SOURCE: The University of Sydney; http://sydney.edu.au/news-opinion/news/2016/05/25/optics-breakthrough-to-revamp-night-vision-.html

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