Building a better infrared sensor: New photodiode design improves responsiveness

Infrared detection is important in a wide range of technologies, from remote controls to autofocus systems to self-driving cars and virtual reality headsets. This means there are significant benefits to be gained by improving the efficiency of infrared sensors such as photodiodes.

Researchers at Aalto University have developed a new type of infrared photodiode that is 35% more responsive at 1.55 μm, an important wavelength for telecommunications, compared to other germanium-based components. Importantly, this new device can be manufactured using current manufacturing techniques, making it very practical for adoption.

“It took eight years from idea to proof of concept,” says Professor Helle Savin of Aalto University.

The basic idea is to create a photodiode using germanium instead of indium gallium arsenide. Although germanium photodiodes are inexpensive and already fully compatible with semiconductor manufacturing processes, so far germanium photodiodes have not performed well in terms of capturing infrared light.

Sabin’s team has successfully created a germanium photodiode that captures nearly all infrared light that reaches it.
The study was published in the journal Light: Science & Applications on January 1, 2025.

“This high performance was made possible by combining several novel approaches: using surface nanostructures to eliminate optical losses and minimizing electrical losses in two different ways.” explains Hanchen Liu, a postdoctoral researcher who built the proof-of-concept device.

The team’s tests showed that the proof-of-concept photodiode was more responsive than existing germanium photodiodes as well as commercially available indium gallium arsenide photodiodes. The new technology captures infrared photons very efficiently and works well over a wide range of wavelengths. The new photodiode can be easily manufactured in existing manufacturing facilities, and researchers expect it to be directly integrated into many technologies.

“The timing couldn’t be better. So many fields now rely on infrared sensing, and this technology has become part of our daily lives,” Sabin said.

Savin and the rest of the team want to know how their technology will impact existing applications, and what new applications the increased sensitivity will enable.