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Nanotube photodectector built at Rice University

04 Mar 2013

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Researchers from Rice University and Sandia National Laboratories have made a breakthrough in optoelectronics by successfully creating a nanotube-based photodetector. This novel device that collects light in and beyond visible wavelengths could pave the way for design innovations in optoelectronic devices, solar cells and possibly specialised cameras.

The Rice detector is based on extra-long carbon nanotubes. At 300µmsµm, the nanotubes are still only about 100th of an inch long, but each tube is thousands of times longer than it is wide.

That boots the broadband detector into what Rice physicist Junichiro Kono considers a macroscopic device, easily attached to electrodes for testing. The nanotubes are grown as a very thin "carpet" by the lab of Rice chemist Robert Hauge and pressed horizontally to turn them into a thin sheet of hundreds of thousands of well-aligned tubes.

They're all the same length, Kono said, but the nanotubes have different widths and are a mix of conductors and semiconductors, each of which is sensitive to different wavelengths of light. "Earlier devices were either a single nanotube, which are sensitive to only limited wavelengths," he said. "Or they were random networks of nanotubes that worked, but it was very difficult to understand why."

"Our device combines the two techniques," said Sébastien Nanot, a former postdoctoral researcher in Kono's group and first author of the paper. "It's simple in the sense that each nanotube is connected to both electrodes, like in the single-nanotube experiments. But we have many nanotubes, which gives us the quality of a macroscopic device."

Rice University photodetector

This illustration shows an array of parallel carbon nanotubes 300 micrometers long that are attached to electrodes and display unique qualities as a photodetector, according to researchers at Rice University and Sandia National Laboratories.

Light detection within and beyond wavelengths
With so many nanotubes of so many types, the array can detect light from the infrared (IR) to the ultraviolet, and all the visible wavelengths in between. That it can absorb light across the spectrum should make the detector of great interest for solar energy, and its IR capabilities may make it suitable for military imaging applications, Kono said. "In the visible range, there are many good detectors already," he said. "But in the IR, only low-temperature detectors exist and they are not convenient for military purposes. Our detector works at room temperature and doesn't need to operate in a special vacuum."

The detector is also sensitive to polarized light and absorbs light that hits it parallel to the nanotubes, but not if the device is turned 90 degrees.

Kono expects many more papers to spring from the collaboration. The initial device, according to Léonard, merely demonstrates the potential for nanotube photodetectors. They plan to build new configurations that extend their range to the terahertz and to test their abilities as imaging devices. "There is potential here to make real and useful devices from this fundamental research," Kono said.

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