Silicon Direct Broadband Semiconductors

 

Researchers at UC Irvine have revealed that certain optical properties can be dramatically strengthened. This change is not from the material itself, but from giving light new properties. 

The scientists showed that by enhancing the speed of incoming protons, it's possible to change how light interacts with matter. Researchers found that the optical properties of pure silicon were enhanced by an astounding four times magnitude. This breakthrough will affect the solar energy sector. 

The study was on the cover of the September issue of ACS Nano. Researchers at Kazan Federal University and Tel Aviv University are working together on this new information.

Dmitry Fishman is senior author and an adjunct professor of chemistry. He states, "In this study, we challenge the traditional belief that light-matter interactions are solely determined by the material. By giving light new properties, we can fundamentally reshape how it interacts with matter. As a result, existing or optically 'under appreciated' materials can achieve capabilities we never thought possible. It's like waving a magic wand- rather than designing new materials, we enhance the properties of existing ones, simply by modifying the incoming light."

Eric Potma is co-author and a professor of chemistry. He reports, " This photonic phenomenon stems directly from the Heisenberg uncertainty principle. When light is confined to scales smaller than a few nanometers, its momentum distribution widens. The momentum increase is so substantial, that is surpasses  that of free-space photons by a factor of a thousand, making it comparable to the electron momenta in materials."

Ara Apkarian is a professor of chemistry. He states, "This phenomenon fundamentally changes how light interacts with matter. Traditionally, textbooks teach us about vertical optical transitions, where a material absorbs light with the photon changing only the electron's energy state. However, momentum-enhanced photons can change both the energy and momentum states of electrons, unlocking new transition pathways we hadn't considered before. Figuratively speaking, we can 'tilt the textbook' as these photons enable diagonal transitions. This dramatically impacts a material's ability to absorb or emit light."

Fishman explained, "Take silicon- for example- the second most abundant element in Earth's crust and the backbone of modern electronics. Despite its widespread use, silicon is a poor absorber of light, which has long limited its efficiency in devices like solar panels. This is because silicon is an indirect semiconductor, meaning it relies on photons (the lattice vibrations) to enable electronic transitions. The physics of light absorption in silicon is such that while a photon changes the electron's energy state, a photon is simultaneously needed to change the electron's momentum state. Since the likelihood of a photon, phonon and electron interacting at the same place and time is low, silicon's optical properties are inherently weak. This has posed a significant challenge for optoelectronics and has even slowed progress in solar energy technology."

Fishman explains further, "Our approach takes a radically different step forward. By enabling diagonal transitions through momentum-enhanced photons, we effectively transform pure silicon from an indirect to a direct bandgap semiconductor without altering the material itself. This leads to a dramatic increase in silicon's ability to absorb light, by several orders of magnitude. This means we can reduce the thickness of silicon layers by the same factor, opening the door to ultra-thin devices and solar cells that could outperform current technologies at a fraction of the cost. Moreover, because the phenomenon does not require any changes to the material, the approach can be integrated into existing fabrication technologies with little to no modifications."

The future of semiconductors is wide open!