Scientists discover new property of light in silicon

Credit: Lucas Van Wyk Joel / UC Irvine.

Researchers from the University of California, Irvine, along with their colleagues at Kazan Federal University in Russia, have made an exciting breakthrough that sheds new light on how light interacts with matter.

This discovery could lead to major advancements in technologies like solar power systems, LEDs, and semiconductor lasers.

Published in the journal ACS Nano, their study explores a previously unknown phenomenon where photons—particles of light—gain significant momentum when trapped within tiny nanoscale structures in silicon, the second-most abundant element on Earth and a cornerstone of modern electronics.

Silicon is traditionally used in electronics but has limited applications in optoelectronics due to its poor optical properties.

Unlike other materials, silicon does not naturally emit light when in its bulk form.

However, when silicon is made porous or structured at the nanometer scale, it can produce light upon exposure to visible radiation—a phenomenon known for decades but not fully understood until now.

The concept of photons having momentum was first recognized by physicist Arthur Compton in 1923, a discovery that contributed to him winning the Nobel Prize.

Compton showed that high-energy gamma photons could interact strongly with electrons, proving that light has both wave and particle properties.

Decades later, Indian physicist C.V. Raman explored similar concepts with visible light, leading to the discovery of the Raman effect used in spectroscopy, although he faced challenges due to the lower momentum of visible photons compared to electrons.

In their groundbreaking experiments, the UC Irvine team found that the momentum of visible light confined in nanoscale silicon crystals can create significant optical interactions. This interaction, termed as “electronic Raman scattering,” is different from the conventional vibrational Raman effect observed by Raman.

It involves changes in the electron states similar to those seen in metals, and it was observed in their lab-made silicon glass samples.

To study this, the researchers used a continuous-wave laser beam focused tightly to create patterns on a 300-nanometer-thick silicon film.

Depending on the temperature achieved during the process, the silicon transformed into either a homogenous cross-linked glass or a heterogeneous semiconductor glass. This allowed the researchers to observe how the electronic, optical, and thermal properties change at the nanometer scale.

Professor Dmitry Fishman from UC Irvine highlighted that this discovery challenges the traditional understanding of light-matter interaction and could significantly enhance the performance of optoelectronic devices.

The matching of electron and photon momentum in disordered systems, similar to what happens with gamma photons in Compton scattering, could now be used to improve optical technologies.

Professor Eric Potma added that this newfound property of light in silicon opens up exciting possibilities for improving devices that convert solar energy and enhance light emission, even from materials previously thought unsuitable for these purposes.

This breakthrough not only advances our understanding of physics but also promises to expand the capabilities of various technological applications in the near future.