New photodetector promises improved imaging, sensing systems

July 02, 2018 // By Rich Pell
Engineers at the UCLA Samueli School of Engineering (Los Angeles, CA) have developed a new type of photodetector - a light (photon) sensor used in cameras and other imaging devices - that they say can work with more types of light than current state-of-the-art such devices.

In fact, say the researchers, their photodetector design eliminates the trade-offs between bandwidth, sensitivity, and speed that are typically seen in current technology. The new photodetector reportedly operates across a broad range of light, processes images more quickly, and is more sensitive to low levels of light than current technology.

"Our photodetector could extend the scope and potential uses of photodetectors in imaging and sensing systems," says Mona Jarrahi, a professor of electrical and computer engineering, who led the study. "It could dramatically improve thermal imaging in night vision or in medical diagnosis applications where subtle differences in temperatures can give doctors a lot of information on their patients. It could also be used in environmental sensing technologies to more accurately identify the concentration of pollutants."

The key to the design of the new photodetector is the use of graphene - a super-thin material made up of a single layer of carbon atoms. Graphene is not only an excellent material for detecting photons - it can absorb energy from ultraviolet light to visible light to the infrared and microwave bands - it is also a very good conductor of electrical current.

To create the photodetector, the researchers laid strips of graphene over a silicon dioxide layer, which itself covers a base of silicon. Then, they created a series of comb-like nanoscale patterns, made of gold, with "teeth" about 100 nanometers wide.

The graphene acts as a "net" to catch incoming photons and then converts them into an electrical signal. The gold comb-shaped nanopatterns quickly transfer that information to a processor, which in turn produces a corresponding high-quality image, even under low-light conditions.

"We specifically designed the dimensions of the graphene nanostripes and their metal patches such that incoming visible and infrared light is tightly confined inside them," says Semih Cakmakyapan, a UCLA postdoctoral scholar and the lead author of the study. "This design efficiently produces an electrical signal that follows

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