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R_Colin_Johnson
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re: IBM debuts CMOS silicon nanophotonics
R_Colin_Johnson   12/13/2010 5:11:40 PM
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For a direct bandgap material, like III-V, an electron near the bottom of the conduction band can recombine with a hole is near the top of the valence band, annihilating the electron and releasing its energy as a photon. Unfortunately, in an indirect band gap material such a process would violate the conservation of crystal momentum.

R_Colin_Johnson
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re: IBM debuts CMOS silicon nanophotonics
R_Colin_Johnson   12/13/2010 4:49:05 PM
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That, of course, is one of the issues that IBM engineers are working on as we speak. And you can bet IBM is also working on process/material/archtectural innovations to overcome the hurdles to silicon emitters.

krisi
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re: IBM debuts CMOS silicon nanophotonics
krisi   12/13/2010 3:38:36 PM
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thank you Colin...this approach seems to be much more practical...but clearly some issues remain, how do you synchronize off chip III-V laser signals with some on chip CMOS generated signals? Kris

R_Colin_Johnson
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re: IBM debuts CMOS silicon nanophotonics
R_Colin_Johnson   12/12/2010 7:31:59 PM
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Yes, Intel has successfully grafted a flake of III-V onto a silicon chip as an emitter, but not in a production environment. I believe that instead of fabricating III-V materials on CMOS chips, that instead IBM is figuring on using a traditional discrete III-V emitter and just piping its emissions onto its CISN chips with fiber optics, where the silicon modulators will take over translating electrical data into optical data.

R_Colin_Johnson
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re: IBM debuts CMOS silicon nanophotonics
R_Colin_Johnson   12/12/2010 7:23:58 PM
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Good emitters need to have a direct bandgap so that electrons in the conduction band can annihilate a hole in the valence band, thereby releasing the excess energy as a photon. Silicon has an indirect bandgap that prevents it from being a good emitter.

krisi
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re: IBM debuts CMOS silicon nanophotonics
krisi   12/11/2010 12:12:08 AM
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No, silicon has indirect bandgap, that is the whole problem...you really have to twist its bonds to produce coherent light...regardless of the wavelength...Kris

R_Colin_Johnson
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re: IBM debuts CMOS silicon nanophotonics
R_Colin_Johnson   12/10/2010 11:58:07 PM
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I thought of this idea of using air-gaps as waveguides when I was interviewing IBM, but then forgot to ask about it. My best guess is that the people working on air-gaps are not in the same huddle as the guys working on silicon photonics. Maybe when both technologies are a little more mature, there will be some cross-fertilization.

R_Colin_Johnson
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re: IBM debuts CMOS silicon nanophotonics
R_Colin_Johnson   12/10/2010 11:52:50 PM
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Intel has many of the components for silicon photonics, including a hybrid emitter that uses a III-V flake, but IBM claims it is the only vendor that has downsized its photonic components enough to make them commercially feasible.

krisi
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re: IBM debuts CMOS silicon nanophotonics
krisi   12/10/2010 11:50:55 PM
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Thank you Colin. Yes, silicon emitter would have poor performance, carbon nanotube based or else (BTW, carbon nanotube laser sounds like a long shot)...and III-V laser would be lower cost, but only if manufactured in III-V process...I think it will be very expensive if manufactured in silicon process, imagine how many process steps will be require to add that laser, enormous complexity, hardly a manufacturable solution! Kris

R_Colin_Johnson
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re: IBM debuts CMOS silicon nanophotonics
R_Colin_Johnson   12/10/2010 11:45:12 PM
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IBM has a silicon emitter, but it is a hybrid that uses a carbon nanotube: htp://bit.ly/eHrLjj However when I asked IBM about it, they said cost-wise no silicon emitter could yet compete with III-V emitters in performance or cost, and until they do no one should switch.

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