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Determine the number density of donor at...

Determine the number density of donor atoms which have to be added to an intrinsic germanium semiconductor to produce an n-type semiconductor of conductivity `5Omega^(-1)cm^(-1)`, given that the mobility of electron in n-type germanium is `3900 cm^(2)V^(-1)s^(-1)`. Neglect the contribution of holes to conductivity.

A

`12xx10^(14)cm^(-3)`

B

`10^(14)cm^(-3)`

C

`8xx10^(15)cm^(-3)`

D

`4xx10^(15)cm^(-3)`

Text Solution

Verified by Experts

The correct Answer is:
C
Here, `sigma=5" mho "cm^(-1),mu_(e)=3900cm^(2)V^(-1)s^(-1)`
As `sigma=e(n_(e)mu_(e)+n_(h)mu_(h))`
Since the density of holes is negligible, so `sigma=en_(e)mu_(e)`
`impliesn_(e)=(sigma)/(emu_(e))=((5" mho "cm^(-1)))/((1.6xx10^(-19)C)(3900cm^(2)V^(-1)s^(-1)))`
`=8xx10^(15)cm^(-3)`
The density of donor atoms is `n_(d)~~n_(e)=8xx10^(15)cm^(-3)`
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