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Carbon Nanotubes Create More Efficient IR Detector

Carbon nanotubes seem to be useful for just about every conceivable application. Their newest purpose is to create highly sensitive uncooled photovoltaic infrared detectors that can be used for industrial, manufacturing, communications and military applications.

A collaboration between Peking University, the Chinese Academy of Sciences and Duke University in Durham, N.C., created an array of single-walled carbon nanotubes (SWCN) and aligned them on top of a silicon substrate. The array was then sandwiched between asymmetric palladium and scandium contacts. These two metals create regions of very low resistance, allowing the device to operate more efficiently.

This schematic shows the design of a single-walled carbon nanotube photodetector, which provides a more efficient method of collecting infrared radiation without relying on expensive cooling. (Image: Sheng Wang, Peking University)

Carbon nanotubes, on top of their myriad optical and electronic properties, can react to infrared light on the order of picoseconds; they are an order of magnitude more efficient than standard semiconductor infrared detectors, which are made from a mercury-cadmium-telluride alloy.

"These nanotubes exhibit strong and broadband infrared light absorption, which can be tuned by selecting nanotubes of different diameters," said Sheng Wang, an associate professor in the department of electronics at Peking University. "Fabrication of carbon nanotube infrared detectors can be readily implemented on a flexible substrate and large wafer at a low cost," he continued.

Semiconductor-based infrared photodetectors normally have to be kept cool using a coolant like liquid nitrogen so that the IR radiation that they emit naturally does not overwhelm the detector. However, detectors made from SWCN emit very little radiation at room temperature and are very good at conducting heat when they do. This allows SWCN IR photodetectors to run uncooled, eliminating the need for complex cooling apparatuses, which makes manufacturing cheaper and easier.

The collaboration found that the new design could be implemented as nanometer-thick film and still achieve a surprisingly high infrared detectivity, whereas traditional detectors require films hundreds of nanometers thick. The manufacturing process is also completely compatible with the process used to create carbon nanotube transistors, so there is no new equipment needed to make the photodetectors.

The team's new goals are to improve the detectivity of the detector with greater SWNT density and to achieve a wide-spectrum response with improved diameter control.

The research was published in a special feature issue of Optical Materials Express, the Optical Society's open-access journal.

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