The Germanium-Tin Laser: Answer to the On-Chip Data Bottleneck?

Silicon-compatible laser could be suitable for data transmission between processor cores, but it's got some problems

2 min read
The Germanium-Tin Laser: Answer to the On-Chip Data Bottleneck?
Illustration: Forschungszentrum Juelich

Photonics engineers dream about using light to zap data between processor cores on multicore CPU chips. By replacing copper wires, such optical interconnects could make chips much faster and more power efficient. The holy-grail for optical on-chip communication is a laser made of silicon.

Now a European research team has built a germanium-tin laser that they say could be used instead. Germanium and tin, like silicon, are group IV elements, which means their crystal layers can be grown directly on silicon. So a germanium-tin laser would be compatible with silicon manufacturing processes.

The proof-of-concept laser, reported in the journal Nature Photonics, operates at-183°C and is powered by light instead of electricity. But the researchers’ eventual goal is to make an electrically pumped laser that operates at room temperature.

One approach for optical interconnects is to make compound semiconductor lasers separately and then bonding them to silicon chips. Intel and Luxtera have, for example, made on-chip communication systems using hybrid silicon/indium phosphide lasers bonded on silicon. But some engineers believe that for mass production creating lasers directly on silicon would be more cost-effective and less error-prone.

The problem with germanium and silicon is that they are bad light emitters, because they have an indirect band gap. When electrons in the materials are excited by light or electricity and then drop back to their lower-energy states, they emit the excess energy as heat instead of light.

Scientists have managed to tease light out of silicon nanowires. And some researchers have engineered germanium’s band gap to make a laser by doping it with phosphorus or putting it under mechanical strain.

The research team from Forschungszentrum Juelich in Germany and the Paul Scherrer Institute in Switzerland gave germanium a direct band gap by alloying it with tin; the resulting material has a tin concentration of 9 percent. They made the laser by growing the germanium-tin layer on a germanium layer that they grew directly on a silicon wafer.

The new laser emits light at a wavelength of 3 micrometers, which the researchers say makes it suitable for detecting carbon compounds as well. And the laser could have other uses, according to the press release:

Gas sensors or implantable chips for medical applications which can gather information about blood sugar levels or other parameters via spectroscopic analysis are examples. In the future, cost-effective, portable sensor technology —which may be integrated into a smart phone—could supply real-time data on the distribution of substances in the air or the ground and thus contribute to a better understanding of weather and climate development.

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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