Choose the correct statements from the following:
A. The resistance of intrinsic semiconductors increases with increase in temperature.
B. Doping pure silicon (Si) with Boron gives p-type semiconductor.
C. The majority charge carriers in an n-type semiconductor are holes.
D. A p-type semiconductor is positively charged.
E. The resistance of a semiconductor decreases when doped with impurities.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → B and E only
Doping adds carriers of one kind, but the crystal as a whole stays electrically neutral.
(A) The resistance of intrinsic semiconductors increases with increase in temperature. — Incorrect. Heating breaks more bonds and increases the number of electron-hole pairs, so the resistance decreases.
(B) Doping pure silicon (Si) with Boron gives p-type semiconductor. — Correct. Boron is trivalent; each atom leaves one bond incomplete, creating a hole (acceptor impurity).
(C) The majority charge carriers in an n-type semiconductor are holes. — Incorrect. In n-type material the majority carriers are electrons; holes are the minority carriers.
(D) A p-type semiconductor is positively charged. — Incorrect. Every hole is balanced by a fixed negative acceptor ion, so the material is neutral.
(E) The resistance of a semiconductor decreases when doped with impurities. — Correct. Doping increases the number of majority carriers enormously, so the conductivity rises and the resistance falls.
NCERT (2026-27):
Temperature Dependence of Resistivity – “… Unlike metals, the resistivities of semiconductors decrease with increasing temperatures.”
Extrinsic Semiconductor – “… When a small amount, say, a few parts per million (ppm), of a suitable impurity is added to the pure semiconductor, the conductivity of the semiconductor is increased manifold.”
n-type Semiconductor – “… Hence in an extrinsic semiconductor doped with pentavalent impurity, electrons become the majority carriers and holes the minority carriers.”
p-type Semiconductor – “This is obtained when Si or Ge is doped with a trivalent impurity like Al, B, In, etc.”
p-type Semiconductor – “… Note that the crystal maintains an overall charge neutrality as the charge of additional charge carriers is just equal and opposite to that of the ionised cores in the lattice.”