Improving the efficiency of light emission to enable laser development from group-IV semiconductors, which provide the leading materials platform of microelectronics, has the potential to revolutionize photonics research and improve everything from on-chip data transmission to biochemical sensing and wireless optical communications.
At Boston University, Professor Roberto Paiella (ECE), Cicek Boztug (PhD ’14), and Faisal Sudradjat (PhD ’12) are collaborating with researchers from the University of Wisconsin-Madison to overcome challenges associated with the radiative properties of silicon, germanium and related alloys, all of which don’t emit light very efficiently due to a basic materials property – their so-called indirect energy bandgap.
They discovered that germanium nanomembranes (i.e., single-crystal sheets no more than a few tens of nanometers thick), when mechanically stressed, can be used to overcome this fundamental limitation and serve as great light emitters, particularly for the mid-infrared spectral region where many biological and chemical species of interest have distinctive absorption lines.
“There have been a lot of efforts to make silicon and germanium efficient photonic active materials,” Paiella said. “Our method has proven to be highly effective.”
The research team wrote a paper on their work titled, “Direct-Bandgap Light-Emitting Germanium in Tensilely Strained Nanomembranes,” and the Proceedings of the National Academies of Sciences of the United States of America recently published their findings.
“We were able to demonstrate that tensilely strained germanium is a good candidate for chip-level integration of electronics and photonics for mid-infrared applications,” said Boztug. “Potentially, this new development could lead to CMOS-compatible biochemical sensors as well as secure free-space communication devices integrated on silicon chips.”
Paiella said that using germanium nanomembranes to emit light is a unique idea in photonics research and that it could enable the development of silicon-compatible diode lasers, which represent the “missing link” for the full integration of electronic and photonic functionalities on the same materials platform.
“If you can make a laser this way, you can integrate laser sources directly on electronic chips,” said Paiella. Potential results could include improved on-chip data transfer and better optical sensing.
For Boztug, working on this project has been eye-opening. Not only did she learn about the mechanical properties of nanomembranes through UW-Madison’s Professor Max Lagally, she also had an opportunity to learn about photonics from for her advisor, Paiella.
“I feel very lucky to have an outstanding advisor like him and realized that I learn something new every time we meet,” she said.
Her research at BU centers around group-IV photonics, an area that she said offers great potential for information processing as well as biological and chemical sensing applications.
“I believe that our studies could lead to a new era for on-chip biochemical sensing applications by combining the well-established silicon microelectronics with our light-emitting germanium membranes,” she said.
-Rachel Harrington (email@example.com)