Funding Supports Modeling and Measurement of Digital Alloys Used to Fabricate Avalanche Photon Detectors

As the digital age has grown into its middle age, we expect to connect and communicate at the speed of light. Discoveries in fiber optics continue to boost the reach, speed and clarity of the signals we send and receive through our electronic devices.

A partnership forged between researchers at the University of Virginia and University of Texas at Austin promises even greater efficiencies in fiber optic telecommunications. Joe C. Campbell, Lucien Carr III Professor of electrical and computer engineering at UVA, and Seth Bank, professor of electrical and computer engineering at UT-Austin, anchor the partnership to design and engineer new materials for avalanche photon detectors.

Their collaboration has produced a device fabricated from a new type of material that detects photons at the right wavelength for telecommunications, up to two microns, with very little noise or static. They discovered that fabricating the detector with a digital alloy yields high efficiencies, or gain, meaning that a single photon creates many electrons in the circuit without amplifying noise. This gain leapfrogs detectors in which the photodiode is composed of conventional semiconductor materials such as silicon. Campbell’s device matches silicon in sensitivity but at 10-times higher speed.

With this discovery comes a mystery. “We have these great detectors, but we don’t know why,” Campbell said. The core problem is randomness and uncertainty. For this type of detector, any give photon can generate any given number of electrons. This variation is a source of background noise that frustrates signal detection and processing.  

To help solve this mystery, Campbell turned to his UVA colleague Avik Ghosh, professor of electrical and computer engineering and professor of physics. “We think the gains that Seth and Joe are seeing are inherent in the material itself, rather than the design of the photodiode or the integrated chip,” Ghosh said.

Ghosh’s team will computationally model the atom-level material changes that occur through layering the alloy’s four elements—aluminum, indium, arsenide and antimonide—and their effect on electron transport and photon gain in the presence of noise, unintended defects, boundary roughness and thermal fluctuations. With this knowledge, Bank and Campbell can make photon detection and gain more predictable, essentially eliminating the background noise. The end result will be an avalanche photon detector that is less error-prone when separating signals from noise.

A $500,000 research grant from the National Science Foundation’s Electronics, Photonics and Magnetic Devices Program, awarded in June 2019 with Ghosh as principal investigator, will add to the team’s modeling and measurement work over the next three years.