Light from silicon proclaimed as ‘Breakthrough of the Year’

In April of this year, TU/e presented a new gamechanger in the chip world: silicon that emits light. For decades it has been regarded as the ‘Holy Grail’ in the microelectronics industry, given that it could make computer chips faster than ever. The physics magazine Physics World recognizes this revolutionary new discovery, and now deems the work of the group of TU/e researcher Erik Bakkers to be the Breakthrough of the Year. The work of the Eindhoven researchers joins other recent noteworthy scientific discoveries in winning the award such as the photo of the black hole (2019), the detection of gravitational waves (2017), and the discovery of the Higgs-particle (2012).

Research leader Erik Bakkers is very proud of the prize, which he wins together with Elham Fadaly and Alain Dijkstra from TU/e, Jens Renè Suckert from the Friedrich-Schiller-Universität Jena in Germany, as well as an international team of collaborators: “We have been working on this for a very long time so it is very nice that we finally managed to succeed; a great achievement by the whole team.”

President of the Executive Board Robert-Jan Smits: “As the board, we are extremely proud of the pioneering work of Erik Bakkers’ group. We think the recognition by Physics World is entirely justified. Erik Bakkers is world leading in the field of nanowires, and his work is fundamental and application-oriented at the same time. It will undoubtedly result in even more breakthroughs that will benefit the entire world.”

Physics World is a publication of the renowned UK Institute of Physics. Every year they proclaim a new physics discovery to be the “Breakthrough of the Year”. Jury member and editor of Physics World Hamish Johnston explains why this research was crowned: “Silicon devices drive our information-based society, but the material’s indirect band gap [an inherent property of the atomic structure, which prevents it from emitting light] has held it back when it comes to telecommunications and other cutting-edge optical applications. By creating a silicon-based material that emits light at telecommunications wavelengths, Bakkers’ team has opened the door to a brand new world of applications for silicon devices.”

This finding in relation to silicon-based devices is timely given that our current technologies, which are predominantly based on electronic chips, are reaching their operational limits. The limiting factor is heat, resulting from the resistance that the electrons experience when traveling through the copper lines that connect the many millions of transistors on a chip. If we want to continue transferring more and more data on our future chips, we need a new technique that does not produce excessive heat associated with resistance.

In contrast to electrons, photons (or light particles) do not experience resistance. As they have no mass or charge, they will scatter less as they travel through a material. However, to use light in chips, a light source is required such as an integrated laser. Silicon is the principle semiconductor material used in the production of computer chips. Unfortunately, silicon is extremely inefficient at emitting light, and so was long thought to play no role in photonics, the chip technology based on light instead of electrons.

The researchers, led by Erik Bakkers, have now succeeded in having silicon emit light in an efficient way. In April of this year, they published a paper in the journal Nature, in which they showed that silicon can form a so-called direct band gap if you grow the material with a hexagonal crystal structure. Bakkers: “The crux is in the nature of the so-called band gap of a semiconductor. If an electron ‘drops’ from the conduction band to the valence band, a semiconductor emits a photon: light.” Nevertheless, 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 for silicon. “By growing the silicon atoms on a hexagonal template, we forced the silicon atoms to grow in a hexagonal structure. That’s how we managed to create a direct band gap and to emit light from silicon,” adds Bakkers.

The researchers believe that creating a laser based on silicon is now just a matter of time. “This would enable a tight integration of optical functionality in the dominant electronics platform, which leads to the potential for on-chip optical communication and affordable chemical sensors based on spectroscopy,” concludes Bakkers.

Erik Bakkers’ research on nanowires goes beyond the development of a silicon-based laser. His laboratory may well realize the world’s first Majorana qubits, the essential ingredient for a superior quantum computer, within a decade or so.

###

Direct Bandgap Emission from Hexagonal Ge and SiGe Alloys, E. M. T. Fadaly, A. Dijkstra, J. R. Suckert, D. Ziss, M. A. J. v. Tilburg, C. Mao, Y. Ren, V. T. v. Lange, S. Kölling, M. A. Verheijen, D. Busse, C. Rödl, J. Furthmüller, F. Bechstedt, J. Stangl, J. J. Finley, S. Botti, J. E. M. Haverkort, E. P. A. M. Bakkers. DOI: 10.1038/s41586-020-2150-y