Power of Germanium
By Rachel Harrington
Improving the efficiency of light emission to allow for the development of lasers from group-IV semiconductors, which provide the leading materials platform of microelectronics, is a goal many photonics researchers are working toward. Such lasers could lead to improvements in everything from on-chip data transmission to biochemical sensing to wireless optical communications.
At Boston University, Associate Professor Roberto Paiella (ECE, MSE), Cicek Boztug (ECE PhD ’14), and Faisal Sudradjat (ECE 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 are excellent materials for electronics but don’t emit light very efficiently.
However, they discovered that germanium nanomembranes—single-crystal sheets no more than a few tens of nanometers thick—when mechanically stressed, can serve as great light emitters, particularly for the mid-infrared spectral region.
“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 published a paper in PNAS on their work titled, “Direct-Bandgap Light-Emitting Germanium in Tensilely Strained Nanomembranes.”
“We were able to demonstrate that germanium can be a good candidate for chip-level integration of electronics and photonics for mid-infrared applications,” said Boztug. “Potentially, this new development could lead to biochemical sensors as well as secure communication devices integrated on silicon chips.”
Paiella said that using germanium nanomembranes to emit light is a unique idea in photonics research, one that 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 include improved on-chip data transfer and optical sensing.
“I believe that our studies could lead to a new era for on-chip biochemical sensing applications by combining well-established silicon microelectronics with our light-emitting germanium membranes,” added Boztug.