Paint-on semiconductor promises cheaper night vision

14 Jul 2006

Researchers have developed a solution-processed photodetector that they claim can outperform costly crystal-grown chips.

Researchers at the University of Toronto have used a "wet" semiconductor to produce photodetectors that are ten times more responsive to infrared light than the sensors that are currently used in military night-vision and biomedical imaging (Nature 442 180).

Making colloidal quantum dots

"Our technology provides a lower cost alternative to achieving ultra-sensitive infrared photodetection for night-vision imaging," Ted Sargent, group leader at the University of Toronto's Department of Electrical and Computer Engineering, told optics.org. "So far we have shown ultrasensitive photodetection across the visible and out to about 1.4 microns."

The researchers made the detectors by first making a solution of semiconductor nanoparticles in extra-pure oleic acid, the main ingredient in olive oil. A drop of the solution was then spin-coated into a film on a glass slide, and patterned with gold electrodes. After placing the film in a solvent for two hours, and then allowing it to evaporate, the team was left with a 800 nm thick layer of light-sensitive nanoparticles.

Semiconductor nanoparticles

The team found that the resulting solution-processed photodetector had a sensitivity in the region of 10¹³ jones, compared with around 10¹² jones for epitaxial InGaAs photo-detectors operating at room temperature.

According to Sargent, such solution-based processing could also have applications in medical imaging, environmental monitoring and fiber-optics communications. This is due to the limited photosensitivity of silicon, which deteriorates from 800 nm and ends abruptly at 1100 nm, and the cost of semiconductors such as InGaAs. In addition, the team claim that in principle the idea could be extended to 2 µm using the current materials system.

Night-vision is made possible by using a focal-plane array of photodetectors that are sensitive to light in the near-infrared (1.3-1.8 µm). Today's night-vision cameras rely on expensive InGaAs-based sensor chips, which means that night-vision cameras typically cost thousands of dollars.

"It's now clear that solution-processed electronics can combine outstanding performance with low cost," added Sergent.