New photodetector could improve night vision, thermal sensing and medical imaging

June 28, 2018 by Amy Akmal, University of California, Los Angeles
The photodetector operates across a broad range of light, processes images more quickly and is more sensitive to low levels of light than current technology. Credit: Jarrahi Research Group/UCLA

Using graphene, one of science's most versatile materials, engineers from the UCLA Samueli School of Engineering have invented a new type of photodetector that can work with more types of light than its current state-of-the-art counterparts. The device also has superior sensing and imaging capabilities.

Photodetectors are light sensors; in cameras and other imaging devices, they sense patterns of elementary particles called photons, and create images from those patterns. Different photodetectors are built to sense different parts of the light spectrum. For example, photodetectors are used in goggles to sense thermal radiation that is invisible to the naked eye. Others are used in cameras that identify chemicals in the environment by how they reflect light.

How versatile and useful photodetectors are depends largely on three factors: their operating speed, their sensitivity to lower levels of light, and how much of the spectrum they can sense. Typically, when engineers have improved a photodetector's capabilities in any one of those areas, at least one of the two other capabilities has been diminished.

The photodetector designed by the UCLA team has major improvements in all three areas – it 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," said 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 study was published in the journal Light: Science and Applications.

The new photodetector takes advantage of the unique properties of graphene, a super-thin material made up of a single layer of carbon atoms. Graphene is an excellent material for detecting photons because it can absorb energy from a broad swath of the electromagnetic spectrum—from ultraviolet light to visible light to the infrared and microwave bands. Graphene is also a very good conductor of electrical current—electrons can flow through it unimpeded.

To form the , 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 convert them into an . The gold comb-shaped nanopatterns quickly transfer that information into a processor, which in turn produces a corresponding high-quality image, even under low-light conditions.

"We specifically designed the dimensions of the nanostripes and their metal patches such that incoming visible and infrared light is tightly confined inside them," said Semih Cakmakyapan, a UCLA postdoctoral scholar and the lead author of the study. "This design efficiently produces an electrical signal that follows ultrafast and subtle variations in the 's intensity over the entire spectral range, from visible to infrared."

Explore further: Graphene photodetector enhanced by fractal golden 'snowflake'

More information: Semih Cakmakyapan et al. Gold-patched graphene nano-stripes for high-responsivity and ultrafast photodetection from the visible to infrared regime, Light: Science & Applications (2018). DOI: 10.1038/s41377-018-0020-2

Related Stories

Graphene photodetector enhanced by fractal golden 'snowflake'

January 16, 2017

(Phys.org)—Researchers have found that a snowflake-like fractal design, in which the same pattern repeats at smaller and smaller scales, can increase graphene's inherently low optical absorption. The results lead to graphene ...

Graphene photodetector integrated into computer chip

September 16, 2013

The novel material graphene and its technological applications are studied at the Vienna University of Technology. Now scientists succeeded in combining graphene light detectors with semiconductor chips.

Developing graphene microwave photodetector

November 25, 2016

A joint team has developed cryogenic microwave photodetector which is able to detect 100,000 times smaller light energy compared to the existing photedetectors. The significance is DGIST have developed the world's first microwave ...

Recommended for you

Graphene helps protect photocathodes for physics experiments

September 17, 2018

Transforming light into electricity is no mean feat. Some devices, like solar cells, use a closed circuit to generate an electric current from incoming light. But another class of materials, called photocathodes, generate ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.