In yet another feat of nano-sorcery, Canadian researchers led by one Edward Sargent have built an infrared detector by spin-coating a glass slide or chip with quantum dots. The process is much higher yield than current low light/IR sensors, leading to potentially lower costs. Pretty impressive, eh? Apparently, the technology could be developed into a form of medical imaging…
SWIR [short wave infrared -ed.] light detection might also be integrated into medical imaging technologies, Sargent says, because SWIR light passes easily through tissue. But silicon cannot absorb SWIR light, which has a wavelength of just one to two microns, so SWIR-detecting technologies have been too expensive to come into wider use.
Existing high-precision SWIR detectors are made up of two chips bonded together. One is a SWIR absorber made of three elements: indium, gallium, and arsenide (InGaAs). The other chip is made of silicon crystals. These detectors are expensive because the two chips are joined with about 100,000 metal connections and it’s difficult to align the silicon crystals in one chip with the InGaAs crystals in the other. “You pay for a low yield,” says Sargent.
Sargent’s chip is what’s called a solution-processed electronic device. A drop of solution containing semiconductors, whether quantum dots or larger organic molecules, is placed on a conductive surface. Quantum dots are semiconducting crystals only a few nanometers across. The chip is spun to distribute the solution, then dried and chemically treated, leaving an even layer of quantum dots. Sargent’s solution includes lead sulfide nanoparticles (measuring four nanometers) and an oily molecule to keep them from clumping together. In a recent Nature paper, Sargent described work in which he demonstrated the detector using a glass slide with strips of gold electrodes as a substrate. It can also be made on a silicon chip.