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Scientists go quantum dotty over night vision

Tailored to the infrared

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US Scientists have found a way to improve the sensitivity of night vision goggles and medical sensors, using a device based on nanostructures called Quantum Dots.

Quantum dots are particularly sensitive to infrared (IR) radiation in between eight and 12 microns. Night vision goggles, military target tracking devices and environmental monitors all use this range of wavelengths, because although the atmosphere is opaque to most IR, in this range it is transparent to it.

The researchers, from the University of Southern California and the University of Texas at Austin, describe the device in the April 24 issue of Physics Letters.

Anupam Madhukar, from USC says "a class of existing infrared detectors are based on what is called 'quantum well' technology. But we have created a detector based on different physics - quantum dot physics - that works at least as well and has the potential to perform better."

The device is based on self-assembled, pyramidal structures, "quantum dots," each no more than 20 nanometres across at the base. These have an indium arsenide core surrounded by gallium arsenide and an indium-gallium arsenide alloy. Varying the exact composition of the dots allows engineers to tailor the device for a range of purposes, from lasers, detectors and optical amplifiers to transistors and tunneling diodes.

"Quantum dots are emerging as the most viable semiconductor nanotechnology for future higher performance communication systems, biomedical imaging, environmental sensors, and infrared detection," said Madhukar.

Although the current performance of the device puts the quantum dots in the mid range, the researchers are confident they can improve the system. They plan to arrange the dot arrays in a configuration called a "resonant cavity". This traps the radiation and bounces it back and forth between mirroring walls, and should make the detector more sensitive. ®

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