Researchers harness single walled carbon nanotubes to improve IR detectors

IR detectors must be continuously cooled to avoid being overwhelmed by stray thermal radiation, so the new design could eliminate the need for expensive and complex cooling systems. The team from Peking University, the Chinese Academy of Sciences, and Duke University says the properties of carbon nanotubes are ideal for infrared applications, so the breakthrough will be useful for industrial, military, manufacturing, optical communications and scientific applications. Sheng Wang, an associate professor at Peking University, commented: "These nanotubes exhibit strong and broadband infrared light absorption, which can be tuned by selecting nanotubes of different diameters. Also, due to their high electron mobility, nanotubes react very rapidly – on the order of picoseconds – to infrared light." The team's photovoltaic infrared detector was formed by aligning SWNT arrays on a silicon substrate, then placing them between asymmetric palladium and scandium contacts. These two metals create an Ohmic contact – a region in a semiconductor that has very low electrical resistance – which helps the detector operate more efficiently. "Fabrication of carbon nanotube infrared detectors can be readily implemented on a flexible substrate and large wafer at a low cost," explained Wang. One of the biggest surprises for the team was achieving relatively high infrared detectivity using a carbon nanotube thin film only a few nanometres thick. Conventional infrared detectors require much thicker films, on the scale of hundreds of nanometres, to obtain comparable detectivity. The team also said that the fabrication process is completely compatible with carbon nanotube transistors, meaning expensive equipment changes will not be necessary. "Our doping free chemical approach provides an ideal platform for carbon nanotube electronic and optoelectronic integrated circuits," noted Wang. The team says it will now focus on improving the detectivity of the detector with greater SWNT density and achieving a wide spectrum response with improved diameter control.