Question

The electrical conductivity of pure semiconductor can be increased by

• A. Increasing the mean life time of charge carriers
• B. Increasing forbidden energy gap
• C. Adding some impurities into it
• D. Sharing conduction band

Hint:

Doping increases the concentration of majority charge carriers, thereby increasing conductivity.
N-type dopants (Group V) add electrons. P-type dopants (Group III) add holes.
Higher temperature also increases conductivity in semiconductors.

Answer 1

The Correct Option is C

Electrical conductivity \(\sigma = q(n\mu_n + p\mu_p)\). 

For a pure (intrinsic) semiconductor, \(n=p=n_i\), which is small.

(a) Increasing mean lifetime: Would increase average carrier density, thus increasing conductivity. However, doping has a much larger effect.

(b) Increasing forbidden energy gap (\(E_g\)): Makes it harder to create electron-hole pairs, so it decreases intrinsic carrier concentration and conductivity.

(c) Adding some impurities into it (Doping): This is the most effective and standard method. It introduces a large number of majority carriers (either electrons for n-type or holes for p-type), significantly increasing conductivity.

(d) "Sharing conduction band": This is unclear and not a standard method to increase conductivity of a given semiconductor material.

The most effective and standard method is doping.

\[ \boxed{\text{Adding some impurities into it}} \]