Medical imaging boost from full-spectrum photodetector

Cancer could be detected sooner following the development of the world’s first photodetector that can see all shades of light.

Artist’s impression of the photodetector device created by RMIT University researchers (Image: Ella Marushchenko)

This is the claim of researchers at RMIT University in Melbourne, Australia, whose broadband photodetector is claimed to be at least 1,000 times thinner than the smallest commercially available photodetector device.

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Photodetectors convert information carried by light into an electrical signal and are used in technologies including gaming consoles, fibre optic communications, medical imaging and motion detectors.

According to RMIT, photodetectors are currently unable to sense more than one colour in the one device and have remained bigger and slower than other technologies that they integrate with.

The RMIT prototype device detects all types of light between deep ultraviolet to near infrared wavelengths, opening new opportunities to integrate electrical and optical components on the same chip.

The breakthrough technology opens the door for improved biomedical imaging, advancing early detection of health issues like cancer.

Study lead author, PhD researcher Vaishnavi Krishnamurthi, said in photodetection technologies, making a material thinner usually came at the expense of performance.

“But we managed to engineer a device that packs a powerful punch, despite being thinner than a nanometre, which is roughly a million times smaller than the width of a pinhead,” she said in a statement.

As well as shrinking medical imaging equipment, the ultra-thin prototype opens possibilities for more effective motion detectors, low-light imaging and potentially faster fibre optical communication.

“Smaller photodetectors in biomedical imaging equipment could lead to more accurate targeting of cancer cells during radiation therapy,” Krishnamurthi said “Shrinking the technology could also help deliver smaller, portable medical imaging systems that could be brought into remote areas with ease, compared to the bulky equipment we have today.”

How versatile and useful photodetectors are depends largely on three factors: operating speed, sensitivity to lower levels of light, and how much of the spectrum they can sense.

Typically, when engineers have tried improving a photodetector’s capabilities in one of those areas, at least one of the other capabilities have been diminished.

Current photodetector technology relies on a stacked structure of three to four layers. The researchers from RMIT’s School of Engineering worked out how to use a nanothin layer on a chip without diminishing the photodetector’s speed, low-light sensitivity or visibility of the spectrum.

A major challenge for the team was ensuring electronic and optical properties did not deteriorate when the photodetector was shrunk, a technological bottleneck that had previously prevented miniaturisation of light detection technologies.

Chief investigator, Associate Professor Sumeet Walia, said the material used, tin monosulfide, is low-cost and naturally abundant, making it attractive for electronics and optoelectronics.

“The material allows the device to be extremely sensitive in low-lighting conditions, making it suitable for low-light photography across a wide light spectrum,” he said.

Walia said his team is now looking at industry applications for their photodetector, which can be integrated with existing technologies such as CMOS chips.

“With further development, we could be looking at applications including more effective motion detection in security cameras at night and faster, more efficient data storage”, he said.

The team’s findings have been published in Advanced Materials.