April 10, 2020 by Luke James
For five decades, researchers around the world have been trying to find a way to make silicon emit light. Now, researchers from Eindhoven University have claimed they've finally done it.
Very quickly, we are approaching capacity with electronic computer chips. If we want higher speeds, we are going to need to find an alternative solution. The main factor limiting current chips is heat. Chips emit heat when they process data because of the resistance that electrons experience when traveling through copper wires.
That’s where light-emitting silicon comes in. With significant achievements in this field, computing could be advanced and chips more efficient. The main benefit that pulsating light does not emit heat since photons do not experience resistance.
Now, researchers from the Eindhoven University of Technology, together with colleagues from the Technical University of Munich and universities in Jena and Linz, are said to have developed an alloy with silicon that is capable of doing just that—emitting light.
Their research, which was published in the journal Nature, describes how they developed their light-emitting silicon-germanium alloys: A breakthrough that could pave the way to photonic computing.
The machine Eindhoven researchers used to grow nanowires with hexagonal silicon-germanium shells. Image Credit: Nando Harmsen, TU/e
Within a standard silicon wafer, silicon atoms are arranged as a cubic crystal lattice. This facilitates electron movement under certain voltage conditions, but it does not allow photons to move, and that is why light cannot easily move through silicon.
Scientists have long since hypothesized that by changing the shape of the lattice to a hexagonal structure would enable photon movement, however, actually creating this has proven challenging. Erik Bakkers, lead researcher on the project, commented that “People have been trying to make hexagonal silicon for four decades and have not succeeded,” and that he and his colleagues have been working on creating a hexagonal lattice for decades.
By using nanowires made of gallium arsenide as a sort-of scaffold, the research team was able to grow silicon-germanium alloy nanowires that have the hexagonal structure that scientists have long been trying to achieve. By adding germanium to the silicon, the wavelength and other optical properties of the light can be fine-tuned for different use cases.
Researcher Elham Fadaly, operating the MOVPE machine. Image Credit: Sicco van Grieken, SURF
Making the silicon-germanium alloy structure emit light was an entirely different challenge, however. Bakkers and his team achieved this by increasing the quality of the silicon-germanium hexagonal shells by reducing the number of impurities and crystal defects.
To test that it could emit light, the structure was then blasted with an infrared laser and the amount of light that made it out on the other side was measured. The amount of energy that was detected coming out of the nanowires was close to the amount put into the system, suggesting that the structure is efficient at transporting photons.
According to Bakkers, the next step for the team is to use the technique to create a tiny laser made from the silicon alloy. Work has already begun on this and the team hopes to have a working silicon laser by the end of 2020.
After a laser has been created, the team will try to find out how to integrate it with conventional cubic silicon computer chips. Bakkers admits that this is a difficult undertaking, “We’re brainstorming to find a way to do this,” he said.
Although Bakkers does not believe that the future of computer chips lays in optics, he and his colleagues have taken a major step toward practical light-based computing.
