

Making the new silicon - user_235711
http://newsoffice.mit.edu/2015/gallium-nitride-electronics-silicon-cut-energy-0729

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zellyn
"CEI’s GaN transistors have at least one-tenth the resistance of such silicon-
based transistors"

To be pedantic, silicon-based transistors also have at least one-tenth the
resistance of silicon-based transistors.

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waterlesscloud
What happened to Gallium-Arsenide? Wasn't that going to replace silicon? Did
it not pan out? Is it used in some cases?

I really know nothing about the state of semiconductor materials, obviously!

~~~
stephen_g
Most of the microwave amplifiers modules (MMICs), mixers, etc. the company I
work for are built on GaAs, and we're starting to use GaN (Gallium Nitride) on
one of our Ka band units (28-31GHz). The GaN parts are quite a bit more power
efficient.

Not exactly sure why the tech is not more widely used though. Funnily enough,
most of the GaN and GaAs devices in general use are LEDs!

~~~
jakub_h
In late 1980s, it was expected that by 2000, you'd have a GaAs computer on
every desktop (powered by Occam or Prolog, of course ;-)). In the end, it
turned out that silicon had more life in it than was expected, while being
much cheaper and easier to manufacture.

~~~
yakshemash
There was also the fact that silicon was already heavily entrenched in the
industry by the time people started to tinker with the possibilities of GaAs
seriously. At least that's what I understood to be the main factor after
listening to Seymour Cray's talk which was posted here some time ago:
[https://www.youtube.com/watch?v=xW7j2ipE2Ck](https://www.youtube.com/watch?v=xW7j2ipE2Ck)
He talks about how difficult it was to convince large suppliers to work with
GaAs at about 30 minutes into the talk.

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zippzom
What is the difference between silicon and gallium nitride that makes silicon
default to off when the circuit is broken and the standard GaN transistors
default to on?

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cyanoacry
It's mostly a function of how the transistors are made. If a transistor is on
by default, they're called "depletion-mode" transistors--this means that the
channel between the two sides of the transistors normally conducts, and via
the control voltage, you deplete that channel of carriers. This is set up by
the "doping" of the channel, which is one of the first steps in the fab
process.

Transistors that are off by default are called "enhancement-mode". GaN
transistors also come in enhancement-mode flavor, so I'm a little surprised by
the article. You can buy them, even as a hobbyist, from EPC. [0]

[0] [http://epc-co.com/epc/Products/eGaNFETs/EPC2023.aspx](http://epc-
co.com/epc/Products/eGaNFETs/EPC2023.aspx)

[1] [http://www.digikey.com/product-
search/en?WT.z_cid=sp_917_011...](http://www.digikey.com/product-
search/en?WT.z_cid=sp_917_0110_buynow&site=us&lang=en&mpart=EPC2023ENG)

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aswanson
Once it becomes economical, with GaN processes pick up where silicon nodes are
right now, or will the whole drive have to start at a less dense node?

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max-a
Great news, but they didn't say anything about selling transistors to the
public. When do you think we can expect to buy those like we do with mosfets?

~~~
Zuph
You can already buy GaN FETs (although not the exact type being researched by
MIT, as mentioned in the article):

\- [http://epc-co.com/epc/Products/eGaNFETs.aspx](http://epc-
co.com/epc/Products/eGaNFETs.aspx)

\- [http://www.ti.com/lsds/ti/power-management/gan-
overview.page](http://www.ti.com/lsds/ti/power-management/gan-overview.page)

You could have a pile of GaN FETs on your desk tomorrow morning, if you really
wanted: [http://www.digikey.com/product-
search/en?pv606=18&FV=fff4001...](http://www.digikey.com/product-
search/en?pv606=18&FV=fff40015%2Cfff8007d&mnonly=0&newproducts=0&ColumnSort=100001&page=1&k=&stock=1&filterAlwaysExpand=1&quantity=1&ptm=0&fid=0&pageSize=100&akamai-
feo=off)

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fsdhlfkasdf
Would this also significantly reduce the heat produced by data centers as less
of the current going through the transistor is converted to heat?

~~~
jakub_h
No, it wouldn't (most likely):
[https://en.wikipedia.org/wiki/Jevons_paradox](https://en.wikipedia.org/wiki/Jevons_paradox)

