Concept:Doping adds neutral impurity atoms to a neutral host crystal lattice, preserving overall electrical neutrality.
Formula:$$q_{\text{total}} = e(p - n + N_D^+ - N_A^-) = 0$$
Solution:- In N-type material, negative free electrons are balanced by an equal number of positive donor ions (\( N_D^+ \)) fixed in the lattice.
- In P-type material, positive mobile holes are balanced by an equal number of negative acceptor ions (\( N_A^- \)) fixed in the lattice.
- Because every mobile charge is balanced by an immobile dopant ion, the bulk semiconductor remains electrically neutral.
Why other options are incorrect:- Options B & C: These confuse mobile majority carrier charge with the net charge of the entire material (which includes the compensating dopant ions).
- Option D: The material is in a stable electrostatic equilibrium with zero net charge.
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