Revolutionary light-emitting silicon

A look inside the Metal Organic Vapor Phase Epitaxy (MOVPE). This machine was used to grow the nanowires with hexagonal silicon-germanium shells. Photo: Nando Harmsen, TU/e.

Breakthrough after 50 years of work paves the way for photonic chips

Emitting light from silicon has been the ‘Holy Grail’ in the microelectronics industry for decades. Solving this puzzle would revolutionize computing, as chips will become faster than ever. Researchers from Eindhoven University of Technology now succeeded: they have developed an alloy with silicon that can emit light. The results have been published in the journal Nature. The team will now start creating a silicon laser to be integrated into current chips.

Every year we use and produce significantly more data. But our current technology, based on electronic chips, is reaching its ceiling. The limiting factor is heat, resulting from the resistance that the electrons experience when traveling through the copper lines connecting the many transistors on a chip. If we want to continue transferring more and more data every year, we need a new technique that does not produce heat. Bring in photonics, which uses photons (light particles) to transfer data.

In contrast to electrons, photons do not experience resistance. As they have no mass or charge, they will scatter less within the material they travel through, and therefore no heat is produced. The energy consumption will therefore be reduced. Moreover, by replacing electrical communication within a chip by optical communication, the speed of on-chip and chip-to-chip communication can be increased by a factor 1000. Data centers would benefit most, with faster data transfer and less energy usage for their cooling system. But these photonic chips will also bring new applications within reach. Think of laser-based radar for self-driving cars and chemical sensors for medical diagnosis or for measuring air and food quality.

DROPPING ELECTRON EMITS A PHOTON

To use light in chips, you will need a light source; an integrated laser. The main semiconductor material that computer chips are made of is silicon. But bulk silicon is extremely inefficient at emitting light, and so was long thought to play no role in photonics. Thus, scientists turned to more complex semiconductors, such as gallium arsenide and indium phosphide. These are good at emitting light but are more expensive than silicon and are hard to integrate into existing silicon microchips.

To create a silicon compatible laser, scientists needed to produce a form of silicon that can emit light. That’s exactly what researchers from Eindhoven University of Technology (TU/e) now succeeded in. Together with researchers from the universities of Jena, Linz and Munich, they combined silicon and germanium in a hexagonal structure that is able to emit light. A breakthrough after 50 years of work.

HEXAGONAL STRUCTURE

“The crux is in the nature of the so-called band gap of a semiconductor,” says lead researcher Erik Bakkers from TU/e. “If an electron ‘drops’ from the conduction band to the valence band, a semiconductor emits a photon: light.” But if the conduction band and valence band are displaced with respect to each other, which is called an indirect band gap, no photons can be emitted – as is the case in silicon. “A 50-year old theory showed however that silicon, alloyed with germanium, shaped in a hexagonal structure does have a direct band gap, and therefore potentially could emit light,” says Bakkers.

Shaping silicon in a hexagonal structure, however, is not easy. As Bakkers and his team master the technique of growing nanowires, they were able to create hexagonal silicon in 2015. They realized pure hexagonal silicon by first growing nanowires made from another material, with a hexagonal crystal structure. Then they grew a silicon-germanium shell on this template. Elham Fadaly, shared first author of the Nature paper: “We were able to do this such that the silicon atoms are built on the hexagonal template, and by this forced the silicon atoms to grow in the hexagonal structure.”

SILICON LASER

But they could not yet make them to emit light, until now. Bakkers team managed to increase the quality of the hexagonal silicon-germanium shells by reducing the number of impurities and crystal defects. When exciting the nanowire with a laser, they could measure the efficiency of the new material. Alain Dijkstra, also shared first author of the paper and responsible for measuring the light emission: “Our experiments showed that the material has the right structure, and that it is free of defects. It emits light very efficiently.”

Creating a laser now is a matter of time, Bakkers thinks. “By now we have realized optical properties which are almost comparable to indium phosphide and gallium arsenide, and the materials quality is steeply improving. If things run smoothly, we can create a silicon-based laser in 2020. This would enable a tight integration of optical functionality in the dominant electronics platform, which would break open prospects for on-chip optical communication and affordable chemical sensors based on spectroscopy.”

In the meantime his team is also investigating how to integrate the hexagonal silicon in cubic silicon microelectronics, which is an important prerequisite for this work. This research project has been funded by the EU project SiLAS, coordinated by TU/e professor Jos Haverkort.

Learn more: Eindhoven researchers present revolutionary light-emitting silicon

Go deeper with Bing News on:

Light-emitting silicon

Professor Hanington's Speaking of Science: The science of light emitting tattoos
on March 5, 2021 at 3:00 pm
I have been writing the Speaking of Science column for 11 years. I have covered just as many different topics as possible in the area of physical science, leaving the ...
An incandescent metasurface for quasimonochromatic polarized mid-wave infrared emission modulated beyond 10 MHz | Nature Communications
on March 5, 2021 at 3:25 am
Incandescent sources are needed for mid-infrared spectroscopy. Here, the authors present a metasurface of nanoheaters that enables fast thermal modulation beyond 10 MHz and emissivity with well ...
What can organic solar cells bring to the table?
on March 3, 2021 at 9:59 am
Silicon solar is suitable for providing large-scale solar ... This improved OSC technology emerged from the field of organic light-emitting diodes, commonly known as OLEDs. OLED technology is used for ...
Scientists Have Invented Light-Up OLED Tattoos
on March 1, 2021 at 6:11 pm
Inspired by bioluminescent organisms, the DIY biohackers at Grindhouse Wetware have unveiled their latest creation — a magnetically activated, LED-equipped silicone implant. The idea of ...
Pumping perovskites into a semiconductor platform
on February 28, 2021 at 4:00 pm
Fluid injection of perovskite semiconductors creates microwires to build different optoelectronic devices on a single silicon chip.

Go deeper with Google Headlines on:

Light-emitting silicon

Go deeper with Bing News on:

Photonic chips

Inverse design of photonic meta-structure for beam collimation in on-chip sensing
on March 5, 2021 at 3:03 am
Most of the existing literature focuses on miniaturizing the optical detection; little attention is directed to on-chip optical excitation. In this work, we design a metasurface to create a planar ...
Photonic chip brings optical quantum computers a step closer
on March 3, 2021 at 9:08 am
Quantum computers promise to deliver enormous computational power and solve problems that cannot be tackled by ordinary (classical) machines. There are many hardware platforms on ...
NIST/Xanadu Researchers Report Photonic Quantum Computing Advance
on March 3, 2021 at 6:31 am
Researchers from the National Institute of Standards and Technology (NIST) and Xanadu, a young Canada-based quantum computing company, have reported ...
Photonics discovery portends dramatic efficiencies in silicon chips
on March 2, 2021 at 6:56 am
A team led by Vanderbilt engineers has achieved the ability to transmit two different types of optical signals across a single chip at the same time.
KVH Industries Reports Fourth Quarter and Full Year 2020 Results
on March 2, 2021 at 3:11 am
KVH Industries, Inc., (Nasdaq: KVHI), a leading provider of innovative, technology-driven connectivity and navigation solutions, today reported financial results for the fourth quarter and full year ...