An intrinsic semiconductor has equal electron and hole concentrations of 6 × 108 m−3. On doping with certain impurity, electron concentration increases to 9 × 1012 m−3. The new hole concentration is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 4 × 104 m−3
In thermal equilibrium the product of the electron and hole concentrations in a semiconductor is constant and equal to the square of the intrinsic concentration. This is the mass action law, and it still holds after doping.
\( \displaystyle n_e n_h = n_i^{2} \)
\( \displaystyle n_h = \frac{n_i^{2}}{n_e} \)
\( \displaystyle n_h = \frac{(6\times10^{8}\,\mathrm{m^{-3}})^{2}}{9\times10^{12}\,\mathrm{m^{-3}}} \)
\( \displaystyle n_h = \frac{36\times10^{16}}{9\times10^{12}}\,\mathrm{m^{-3}} \)
\( \displaystyle n_h = 4\times10^{4}\,\mathrm{m^{-3}} \)
Note: A similar question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 1).