Q. 12

# Estimate the prop

Answer :

Given:

Since, the number conduction electron and holes are the same,

∴ Number of charge carriers initially

On adding the impurity to the pure silicon the conductivity becomes 100 times the initial , therefore the total charge carriers should become

(∵ σ is directly proportional to concentration of charge carriers)

Let be the holes after adding the impurity and will be the electrons

Now, the product of the total conduction electrons and holes remains nearly constant,

∴

Solving for by discriminant method,

We get

Rejecting the second value on the basis of the fact that the initial number of holes must be smaller than the number of holes after doping.

∴ the number of holes or boron atoms added

Ratio of number of silicon atom to boron atom

∴ boron must be added in proportion of 1 boron atom in 3.59× 10^{10} silicon atoms.

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