Consider the following statements about silicon doped with a pentaval…

The correct answer is Option (3) → (A), (B) and (C) only

In n-type silicon, the fifth electron of each donor atom is very weakly bound. Thermal energy at room temperature is enough to set it free.

(A) The fifth electron of a phosphorus atom needs only about 0.05 eV to become free. — True. The four bonded electrons act as part of the core for the fifth electron. So its ionisation energy is very small, about 0.05 eV in Si.

(B) The number of electrons given by the donor atoms does not change with a rise in temperature. — True. Almost every donor atom is already ionised at room temperature. So this number depends on the doping level only.

(C) The number of free electrons produced by the Si atoms increases weakly with temperature. — True. These electrons come from broken Si–Si bonds. A few more bonds break as the temperature rises.

(D) The dopant atom is chosen to be much larger in size than the silicon atom. — False. The dopant must not distort the silicon lattice. So its size must be nearly the same as that of a silicon atom.

NCERT (2026-27):
n-type semiconductor – “… For example, the energy required is ~ 0.01 eV for germanium, and 0.05 eV for silicon, to separate this electron from its atom. …”

n-type semiconductor – “… The number of electrons made available for conduction by dopant atoms depends strongly upon the doping level and is independent of any increase in ambient temperature. On the other hand, the number of free electrons (with an equal number of holes) generated by Si atoms, increases weakly with temperature.”

Extrinsic Semiconductor – “… A necessary condition to attain this is that the sizes of the dopant and the semiconductor atoms should be nearly the same.”