Momentum-engineered photonic states make bulk silicon shine

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An international team of researchers, led by scientists from the University of California, Irvine, has demonstrated a fundamentally new way to make silicon emit light—overcoming one of the most persistent limitations in modern electronics and photonics. In their work appearing in Nano Letters, the scientists show that silicon, long considered an inefficient light emitter due to its indirect bandgap, can be transformed into a bright, broadband source. The researchers produced emissions from silicon in its conventional bulk form, without modification to its composition or structure. Instead, the breakthrough comes from modifying the properties of light itself.

"Silicon has been the foundation of electronics for decades, but its inability to efficiently emit light has remained a major obstacle for photonics," said Dr. Aleks Noskov, first author of the study. "What we demonstrate here is a fundamentally different approach. Rather than changing the material, we change the light. And that opens entirely new pathways for how silicon can interact with it."

In conventional optics, photons carry very little momentum compared to electrons in a solid. This mismatch prevents efficient light emission in silicon, as radiative recombination requires both energy and momentum conservation. As a result, silicon relies on phonons, vibrations of the crystal lattice, to assist in the emission, making the process extremely inefficient.

The scientists found that this limitation can be removed when light is confined to extremely small, nanometer-scale dimensions. In such a highly confined state, the momentum spectrum of photons significantly broadens, reaching values comparable to those of electrons in the material.

"Photon momentum is no longer negligible," explained Prof. Dima Fishman, senior author on the study, "which puts it on par with electron momentum in the semiconductor. This allows optical transitions in silicon that normally require phonons to occur directly, without any assistance."

Engineering extreme light confinement on silicon

Experimentally, the team achieved this extreme confinement by decorating silicon surfaces with ultrasmall, sub-2-nanometer metal particles. Under illumination, the silicon surface began to emit intense, ultrabroadband light spanning the visible and near-infrared spectral range.

Remarkably, the emission appears insensitive to the material origin of the surface decorations, indicating that the effect is governed primarily by the degree of spatial light confinement rather than the material's chemistry. Moreover, the emission efficiencies approach those of conventional direct-bandgap semiconductors—an extraordinary result for bulk silicon.

"This is a complete shift in how we think about light–matter interactions," said Prof. Eric Potma, another senior author of the study. "Traditionally, optical transitions in materials are considered fixed by their electronic structure. Here, we show that by engineering the momentum of light, we can reshape those rules and enable entirely new radiative pathways."

Rewriting the rules of light emission

The implications extend far beyond a single material. By enabling so-called "diagonal" transitions, where both energy and momentum change simultaneously, the approach effectively bypasses the fundamental constraint that has limited indirect semiconductors for decades. In silicon, this results in the emergence of a new radiative recombination channel that outcompetes both conventional emission and non-radiative losses.

"This work builds on our earlier findings in absorption, but goes a crucial step further," Potma added. "We are now showing that the same physical principle enables efficient emission. In other words, we are opening a new regime where light can directly control electronic transitions in materials."

The discovery lays the groundwork for fully integrated silicon photonics, where light sources, detectors, and electronic components can coexist on the same platform. Such integration has long been a goal for technologies ranging from optical communications to neuromorphic and photon-driven computing.

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Broader impact on future photonics

Beyond silicon, the concept of momentum-engineered photonic states may apply broadly to other materials where optical transitions are restricted by momentum conservation. By conditioning light rather than redesigning materials, the approach offers a scalable and potentially transformative route for optoelectronic device engineering.

"We are only beginning to explore what becomes possible when photon momentum becomes an engineerable parameter," Fishman said. "This could fundamentally change how we design optical technologies."

As the researchers continue to develop silicon-based light-emitting devices based on this principle, their findings point toward a future where the long-standing divide between electronics and photonics may finally be bridged, using the same material that already underpins the modern technological world.

Publication details

Aleksei I. Noskov et al, Overcoming the Indirect Band Gap: Efficient Silicon Emission via Momentum-Engineered Photonic States, Nano Letters (2026). DOI: 10.1021/acs.nanolett.6c00596

Journal information: Nano Letters

Key concepts

siliconOptics & lasersOptical materials & elementsSemiconductors

Provided by University of California, Irvine