Research Reveals How Staircase Photodetector Amplifies Signals with Low Noise

By Karen Walker

Adam Dadey, a Ph.D. student of electrical engineering at the University of Virginia School of Engineering and Applied Science, earned the top student paper award at the 2021 IEEE Photonics Conference for his contributions to three- and five-step staircase avalanche photodiodes.

Dadey fabricates and then characterizes the properties and performance of avalanche photodiodes for imaging systems and related applications, alongside members of the photonic devices group led by Joe Campbell, Lucien Carr III professor of electrical and computer engineering.

Dadey’s paper, Cryogenic Noise of Staircase Avalanche Photodiodes, reports on the group’s advances in photodetectors that perform well in the visible and near-infrared light spectrum. These so-called staircase photodetectors rely on semiconductor-based avalanche photodiodes, a technology for which Campbell has led pioneering, standard-setting research.

The team’s avalanche photodiode achieves high efficiencies or gain — meaning that a single photon creates many electrons — with the lowest amplifying noise ever reported. Dadey’s research has helped the team pinpoint and control this process, removing randomness and reducing noise.

Campbell’s group, in collaboration with Seth R. Bank, Cullen Trust Professor at UT-Austin, is the first to successfully demonstrate this novel detector that was first proposed 35 years ago but never before realized.

“This is exciting work that has the potential to be a game changer for applications as diverse as optical communication networks, next-generation imaging systems and ‘vision’ for autonomous vehicles,” Campbell said.

Adam Dadey and Joe Campbell in labAdam Dadey and Professor Joe Campbell fine tune the alignment of a test device in a high-vacuum cryogenic chamber.

Adam Dadey and Professor Joe Campbell fine tune the alignment of a test device in a high-vacuum cryogenic chamber.

Dadey has always been fascinated with diodes and their ability to channel and control electric current. He pursued his interest as an undergraduate at the University of Delaware, earning a Bachelor of Electrical Engineering degree.  

Dadey’s undergraduate experience allowed him to conduct research in photonics - how to generate, detect and manipulate light - with opportunities in multiple applications in telecommunications, medicine, astronomy and atmospheric sciences.

Through this program, Dadey learned to work with photodetectors designed by Campbell and Andreas Beling, professor of electrical and computer engineering at UVA.

“It’s cool to be able to make an actual device that you’ve learned so much about in class, to see the theories in action,” Dadey said.

When Dadey began looking at Ph.D. programs, his familiarity with devices developed at UVA prompted him to reach out to Campbell. Dadey selected UVA and joined Campbell’s group in 2020. Dadey is now making the transition to his dissertation research and will continue to push the boundaries on APD technology.

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