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Light Emitting Silicon Steps It Up
h4mm3r writes "STMicroelectronics plans to announce a breakthrough on Monday in light-emitting silicon that could lead to a new generation of more powerful computing processors and more efficient automobile components as well as
potentially higher-speed optical data-transmission systems. (gotta register, free yadda yadda)"
Being able to integrate light emitting semiconductor devices together with electronic circuits is one of the holy grails of the semiconductor industry. Not only would the benefit come to increasing the speed of processors, optoelectronic devices would benefit greatly from this technology through integration. The cost savings and increased functionality would be incredible. Can't wait for it to become a reality.
"It's comin' back around again..." -RATM
One of the things this article really doesn't elaborate on is just how difficult the road has been to make efficient light emitting silicon. I had a professor as an undergraduate at the University of Rochester who spent a significant amount of time trying to get it to work. The article doesn't go into the technology, but I'm guessing they're using porous silicon. Porous-Si has small nanometer scale pores in (etched via electochemistry). The pores effectively alter the band gap of the silicon, increasing it to that of the compound light-emitting semiconductors such as GaAs. While this technique works well at generating light, the problem is getting it to generate light efficiently. Hence the exotic rare-earth materials such as erbium. I'm impressed that STMicroelectronics was able to increase the light output 100-fold. Extravagent claims such as these make me want to take a wait-and-see attitude. The process might be so difficult that it wont be practicle on high-performance chips for some time. Also, the processing techniques of light emitting silicon is different than for standard logic. I'd like to see how well these two processes can be merged.
Here's something else (only slightly different):E G20021028S001 4
http://siliconstrategies.com/story/O
Basically, LEDs use Gallium and some other material because Silicon is horribly inefficient at photo-applications (its a electron band-gap thing, ask a physicist), but because its so cheap and GaAs is very not cheap, they still use polycrystalline Si for large solar cells.
Unfortunately, Leds are just too dim when silicon is used, so Gallium and whatever else (depends on wavelength) is still necessary there. By getting efficient light emitting Silicon, a whole pantload of money gets saved by avoiding Gallium.
End note: Why is Si cheaper than Ga? Refinement is more complex for Ga, Si is much more plentiful, and it hard to make large wafers of GaAs. Plus GaAs oxide (don't know the formula) is liquid at room temperature, so the only demand is photo applications (and stressed Si) because making IC with just GaAs means you can't use a liquid GaAs-oxide as a mask/gate/whatever.
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The AC that replied to you pointed out the possible benefits for solar cells, but...
The reason the Sun designer described it as "the holy grail" is timing circuitry on CPU's. What's the figure, something like 75-80% of a CPU is dedicated to timing circuitry? Think about what happens when you replace all that timing circuitry with a light pulse, and just pick it up wherever you need it. Eliminate all the wiring currently used to distribute the timing, and you get lower power, tons more silicon to devote to other things, and probably the potential for speed gains.
Wow, sorry but I need to correct you on a bunch of points.
Gallium Arsenide (not gallium) is used to make a variety of LED and semiconductor lasers. Silicon is unattractive for light-emitting applications because it has an indirect bandgap, making emission of photons much less efficient than in direct bandgap materials.
Making large wafer of GaAs is not so much a processing issue as a cost issue (i.e. how much would one wafer end up having to sell for, and would anyone at all even think of dropping that much money on one). HOWEVER, neither GaAs nor its native oxide(s) are liquid or even water-soluble at room temperature. You were perhaps thinking of Germanium. The problem with GaAs oxides is that they do not form into such nice layers as SiO2, and that they do not effectively passivate the GaAs surface such that MOSFETs cannot be fabricated. GaAs (and InP) and still widely used (in your cellphone for example), but in different ways than silicon and not nearly as widely as silicon.