Identify the correct statements among the following.
(A) The number of electrons (\( n_e \)) is more than the number of holes (\( n_h \)) in intrinsic conductors.
(B) Semiconductors are elements (Si, Ge) type as well as compounds (GaAs, CdS).
(C) The number of charge carriers can be changed by ‘doping’ of a suitable impurity in pure semiconductors.
(D) Holes are essentially electron vacancies in a valence band.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B), (C) and (D) only
In a pure (intrinsic) semiconductor, every electron freed from a covalent bond leaves one hole behind, so electrons and holes are produced in pairs.
(A) The number of electrons (\( n_e \)) is more than the number of holes (\( n_h \)) in intrinsic conductors. — Incorrect. Pair generation gives \( n_e = n_h = n_i \) in an intrinsic semiconductor; \( n_e \gt n_h \) holds only in an n-type (doped) semiconductor.
(B) Semiconductors are elements (Si, Ge) type as well as compounds (GaAs, CdS). — Correct. Si and Ge are elemental semiconductors; GaAs and CdS are compound semiconductors.
(C) The number of charge carriers can be changed by ‘doping’ of a suitable impurity in pure semiconductors. — Correct. Doping with a pentavalent or trivalent impurity raises the number of electrons or holes by a large factor.
(D) Holes are essentially electron vacancies in a valence band. — Correct. A hole is the vacancy left in the valence band when an electron leaves a bond; it behaves like a positive charge.
Statements (B), (C) and (D) are correct, which is Option (4).
NCERT (2026-27):
Summary – “… 4. Semiconductors are elemental (Si, Ge) as well as compound (GaAs, CdS, etc.).”
Summary – “… The number of electrons (ne) is equal to the number of holes (nh) in intrinsic conductors. Holes are essentially electron vacancies with an effective positive charge.”
Summary – “… 6. The number of charge carriers can be changed by ‘doping’ of a suitable impurity in pure semiconductors.”