Researchers at the University of Michigan have developed a semiconductor device that uses laser light to direct the movement of electrons without the need for an applied electric field or power source.
The device was designed primarily to investigate fundamental physics and demonstrate behavior that had never been observed before. But this discovery could ultimately support technologies that combine optics and electronics, including advanced sensing, imaging, and telecommunications. It could also lead to better ways to send signals between devices and encode more information within them.
“This electrical device that we produced at the Lurie Nano Fabrication Facility has the potential to be turned into a device that measures various aspects of light,” said Yiming Gong, who helped lead the project as a doctoral student in the UM Department of Physics. “But this comes from a very fundamental level of physics: interference between different light absorption processes.”
Direct electron flow of two-color light
With federal support from the National Science Foundation, the research team demonstrated that two different colors of light can generate an organized flow of electrons through a semiconductor. The researchers were also able to change the direction of the current by rotating the polarization of the two light fields, which represent the direction of vibration of the light waves.
“This is not normal behavior. If you think about electrons moving through a material, you apply an electric field that causes them to move and actually bounce or drift through the material. Here, using light, you can actually shoot the electrons in a particular direction without applying an electric field,” said UM physicist Stephen Cundiff, senior author of the team’s new report published in the journal Science. physical review letter.
Early research had already shown that light alone could move electrons. The new experiment goes further by creating a narrow stream of electrons and controlling the precise direction in which the electrons travel.
“Lights are no longer just turning on electrical current, they’re also targeting it,” Cundiff said.
lighthouse light made of electronics
Cundiff likens this effect to a lighthouse whose lamp rotates, spreading its light across the horizon. However, in this experiment, the moving beam consists of electrons. Scientists can rotate that electron beam by adjusting the polarization of two phase-coherent light fields.
The effect depends on quantum interference. This occurs when two colors of light travel through a semiconductor through different absorption paths, ultimately leading to the same final state. Light delivers energy into matter in discrete or quantized packets known as photons. These photons move charge carriers in the semiconductor.
In the UM setup, the material absorbs the incident light through two paths simultaneously. Cundiff compared the process to ripples overlapping each other. For electrons moving in one direction, the ripples line up and reinforce each other. For electrons moving in other directions, the electrons cancel each other out.
This selective strengthening produces a current that is concentrated in a specific direction rather than spread uniformly throughout the material.
Quantum devices long predicted become reality
JE Sipe of the University of Toronto, who worked with the researchers on a previous project, predicted that such an “electronic lighthouse” could be created. Gong eventually turned his theoretical idea into a practical device with the help of the Lurie Nano Manufacturing Facility.
“LNF is an amazing facility,” Gong said, adding that fusing the device’s materials together in a way that did not create extraneous electric fields was a painstaking process.
Preventing unnecessary electric fields was especially important because the researchers needed to ensure that the flow of electrons came entirely from light. Manufacturing this device required Gong and the facility’s staff to experiment with different manufacturing methods.
“This was the biggest mystery for me to solve, because there is no standard method, so I worked with the LNF staff to experiment with different recipes and temperatures and come up with a manufacturing process.”
Kai Wang, a former postdoctoral fellow who worked with Cundiff and is now a professor of electronic information and electronic information at Sun Yat-sen University in China, also advised Gong during the project.
Gong went on to earn a PhD at UM and now works as a machine learning scientist in Chicago. In that role, he applies the quantitative and analytical skills he developed during his research in physics to machine learning problems.
