Illustrating showing two colored laser pulses moving an electron beam in different directions. (Image Credit: Yiming Gong/University of Michigan)
University of Michigan engineers recently developed a device that uses laser light to control electron flow via a semiconductor without a power source. This device is designed to study fundamental physics and reveal a new physical phenomenon. Other technologies that combine optics and electronics could use it for sensors, imaging, and telecommunications.
With this technology, signal-to-device transmission could also improve while enabling more data storage in the signals. "This electrical device that we manufactured at the Lurie Nanofabrication Facility has the potential to turn into something that measures different aspects of light," said Yiming Gong, who helped lead the project as a doctoral student in the U-M Department of Physics. "But this originates from a very fundamental level of physics, which is the interference between different optical absorption processes."
By beaming two different colors of light on a semiconductor, the team proved it’s possible to control electron flow in a specific direction. Shifting the two phase-coherent optical fields’ polarization enabled the team to direct the electronic current.
"This isn't the way things normally work. When you think about electrons moving through a material, they're moving because you've applied an electric field and they actually bounce around and drift across the materials. Here, using light, you can actually sort of squirt the electrons in a specific direction without applying an electric field," said U-M physicist Steven Cundiff, senior author of the team's PRL report.
This effect relies on quantum interference, which occurs when two colors of light cause electrons to reach the same final state through different absorption pathways. As the semiconductor absorbs light, its energy excites electrons, setting them in motion. That energy is transferred in discrete packets called photons.
In the team’s setup, light is absorbed through two pathways simultaneously. These routes strengthen each other for electrons moving in a certain direction. However, they offset each other when electrons move in different directions.
The team says it was challenging to meld the device’s materials together without extraneous electric fields emerging. "That was the biggest puzzle to solve for me, because there isn't a standard way to do that. So I worked with the LNF staff to play around with different recipes and temperatures to come up with a manufacturing process," Gong said.
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