For the first time, scientists at the Institute of Photonic Sciences (ICFO) have managed to create a digital imaging sensor that can capture ultraviolet, infrared and visible light at the same time. What wonder materials are behind this breakthrough? No prizes for guessing it's two of the usual suspects: graphene and quantum dots.
Both of these materials have long individual lists of potential applications, and when you pair them up, that list grows even longer. But in this case, we're not talking about quantum dots made of graphene – the ICFO team used metallic, PbS colloidal quantum dots deposited onto a sheet of graphene. This hybrid system was then deposited onto a complementary metal-oxide semiconductor (CMOS) wafer, and hooked up to image sensor dies and a read-out circuit.
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The end result is a high resolution image sensor that's sensitive to a huge range of wavelengths, from UV rays of about 300 nm, through the visible spectrum in the middle, and up to infrared light with a wavelength of 2,000 nm. The researchers say this is the first time that a single image sensor has been capable of detecting light across such a wide spectrum at once.
"We engineered the quantum dots to extend to the short infrared range of the spectrum (1100-1900 nm), to a point where we were able to demonstrate and detect the night glow of the atmosphere on a dark and clear sky enabling passive night vision," says Gerasimos Konstantatos, co-author of the study. "This work shows that this class of phototransistors may be the way to go for high sensitivity, low-cost, infrared image sensors operating at room temperature addressing the huge infrared market that is currently thirsty for cheap technologies."
Historically, CMOS systems don't integrate easily with semiconductors other than silicon, so getting them to work with graphene is another first for ICFO's new sensor. Even better, the team says the device can be built fairly easily and cheaply at room temperature, which should help keep production costs down and expand their possible commercial applications.
"The development of this monolithic CMOS-based image sensor represents a milestone for low-cost, high-resolution broadband and hyperspectral imaging systems," says Frank Koppens, co-author of the study. "In general, graphene-CMOS technology will enable a vast amount of applications, that range from safety, security, low cost pocket and smartphone cameras, fire control systems, passive night vision and night surveillance cameras, automotive sensor systems, medical imaging applications, food and pharmaceutical inspection to environmental monitoring, to name a few."
The research was published in the journal Nature Photonics.