dopping concentration of semiconductors

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vivek.raunak

Joined Oct 23, 2010
29
hiii
while revising basic electronics through beginning one question arose in my mind..
as mentioned..doping concentration of n-type n p-type impurity is 1 in 10 million of pure semiconductor....
why the ratio is too law?
is there any problem with high concentration???
we could have been increase conductivity of semiconductor by increasing doping concentration.
 

Papabravo

Joined Feb 24, 2006
12,301
In terms of counting atoms 10 million is insignificant. It is precisely those concentrations that turn an intrinsic(pure) semiconductor into the more useful form. From the page for silicon:

http://www.webelements.com/silicon/

we see that 28.0855 grams contains 6.02E23 atoms of silicon. You impurity concentration of 1 part in 10 million (1E7) that from that sample of silicon there will be 6.02E16 impurity atoms. That is more impurity atoms than dollar in the US National debt by several orders of magnitude. If Boron was used as the impurity that would amount to 108 micrograms of boron to our 28 grams of silicon.

http://www.webelements.com/boron/
http://www.webelements.com/
 

kubeek

Joined Sep 20, 2005
5,587
we could have been increase conductivity of semiconductor by increasing doping concentration.
Yes, but you want it to be semiconductive, not conductive all the time which will probably happen with too high doping concentration.
 

Papabravo

Joined Feb 24, 2006
12,301
Yes, but you want it to be semiconductive, not conductive all the time which will probably happen with too high doping concentration.
They do use higher than normal concentrations (parts per thousand) as a substitute for metal.
 
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