Glowing Silicon Nanowire Reveals How to Put Optics in Your CPU
upstart writes in with an IRC submission for SoyCow8192:
Glowing silicon nanowire reveals how to put optics in your CPU:
The key term in integrated circuits is integrated. The ability of fabrication facilities to integrate things sets limits on what processes are available, and what materials can be safely used. As soon as you suggest a different material or process, the whole chain is broken, and anybody suggesting it should expect people questioning your suitability for your current position. "Compatibility" is why you will not find laser-powered integrated circuits in your laptop.
The ability to make lasers using integrated-circuit-compatible materials, however, may have gotten a boost, with a demonstration of glowing (but not yet lasing) silicon.
Optics and lasers are the backbone of high speed data transmission. You do not use copper wires to transport data at 1Tb/s. Instead you will use glass and some finely tuned and very expensive laser diodes. But laser diodes are made using processes and materials that are not compatible with those used to make integrated circuits. So, while it is possible to create, say, an optical interconnect between a RAM module and a CPU, you have to somehow glue the optics to the silicon chip in exactly the right location. Research labs are happy to sacrifice PhD students to such ventures, but PhD-bots don't scale well, are high maintenance, and their deployment leads to dark looks.
A better solution would be to get silicon to emit light, but it really doesn't like doing that. The reason is not that complicated, but does take a few words to explain.
[...] To get silicon glowing, the researchers turned to alloys. A cool thing about semiconductors is that their optical and electronic properties tend to smoothly change when you alloy them. If you add germanium to silicon, the resulting alloy will start showing some of the characteristics of germanium. However, while some properties can be adjusted continuously, others cannot. A band-gap is either direct or indirect, not a mixture. So, how much germanium does it take to make silicon glow?
The answer turns out to be about 65 percent.
Journal Reference:
Elham M. T. Fadaly, Alain Dijkstra, Jens Reni Suckert et al. Direct-bandgap emission from hexagonal Ge and SiGe alloys, Nature (DOI: doi:10.1038/s41586-020-2150-y)
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