[SI-LIST] Re: Doping effects.
- From: Ed Sayre III <esayre3@xxxxxxxx>
- To: justin.tabatchnick@xxxxxxxxx
- Date: Fri, 21 Mar 2003 13:03:26 -0500
Justin,
You are correct about the electron locations. I stated, "acting like a
metal", not "is a metal" because the resistivity drops thus more conductive
(like a metal) and less like an insulator. I know this is splitting hairs,
but it was the overall point I was trying to make without an extensive
amount of theory.
Regards
-Ed
At 09:00 AM 3/21/2003 -0800, you wrote:
>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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