[SI-LIST] Re: Doping effects.
- From: "Tabatchnick, Justin" <justin.tabatchnick@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 21 Mar 2003 09:00:14 -0800
Hi Ed;
I don't understand what you mean by the doping becoming degenerate and
acting like a metal can you be more explicit. If I am correct the
dopant does not have free electrons (they still reside in the valence
band) and a metal does (electrons reside in the conduction band).
Thanks
Justin
-----Original Message-----
From: Ed Sayre III [mailto:esayre3@xxxxxxxx]=20
Sent: Friday, March 21, 2003 7:45 AM
To: rfengg@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Doping effects.
Hi George,
A question right up my alley! When you dope a semiconductor you are
just providing more free electrons or holes, dependant on the dopant, to
reduce the resistivity. This is illustrated by the increases the drift=20
current through the material., At some point the doping becomes
degenerate,=20
at which time the material is less silicon and more dopant. Basically=20
increasing the doping of a semiconductor makes it behave more like a
metal,=20
to the point of degeneracy then it changes back.. This method of=20
degenerate doping can also be used to create an insolating layer in a=20
silicon substrate for isolation.
There are a very limited number of pure metals that are=20
superconductors, Niobium the most commonly used and the one with the=20
highest transition temperature, 4K. Others are Aluminum and Tin. The=20
transition temperature is the temperature at which a material becomes=20
superconducting. If you look at a resistivity versus temperature plot
of=20
most materials and extrapolate to 0 K the resistivity does not go to
zero=20
at 0 K, even superconductors above Tc. A superconductor will look like
a=20
normal metal then transition, in a step wise fashion(the transition=20
region), to 0 resistance, at Tc, under DC conditions.
Since we use the interconnects of a chip, package, or system at=20
frequencies other than DC there is also another interesting=20
behavior. Superconductors actually have measurable loss at frequencies=20
above DC. These losses become significant and then pass those of cooled
Copper or Aluminum at about 100GHz for temperature of 77K (Liquid=20
Nitrogen). So the interesting thing is that cryo-cooled normal metals=20
actually perform better at high frequencies than high temperature or low
temperature superconductors. Ramo, Whinnery and VanDuzer, 3rd edition,=20
have an excellent plot of this on page 152 figure 3.16b.
BTW, this was one of the areas of my research. Hope this helps.
Regards
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NORTH EAST SYSTEMS ASSOCIATES, INC
-------------------------------------=20
"High Performance Engineering & Design"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Edward Sayre 3rd e-mail: esayre3@xxxxxxxx
NESA, Inc. http://www.nesa.com/
5 Lan Drive, Suite 200 Tel +1.978.392-8787 x 218
Westford, MA 01886 USA Fax +1.978.392-8686
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
At 03:30 PM 3/21/2003 +1100, you wrote:
> Hi all,
> If doping increases the conductivity of Silicon , why cant
we=20
> attain superconductivity with heavy doping of a material? Whats the=20
> phenomenon that limits the conductivity if we actually do increase=20
> carriers by doping?
>
>Thanks and regards,
>George.
>
>
>
>_____________________________________________________________
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