Concept:When a neutral pentavalent donor atom (e.g., Phosphorus) loses its fifth valence electron to the conduction band, its atomic core is left with a net positive charge and remains fixed in the crystal lattice.
Formula:$$\text{Donor Ionization: } N_D^0 \longrightarrow N_D^+ + e^-$$
Solution:- The donated free electron is mobile and can conduct electricity.
- The remaining donor nucleus and inner-shell electrons have a net positive charge (\( N_D^+ \)) and are locked into the covalent lattice structure.
- Therefore, the immobile species in an N-type semiconductor are positive donor ions.
Why other options are incorrect:- Option B: Negative acceptor ions (\( N_A^- \)) are the fixed species in P-type semiconductors.
- Option C: Free electrons are mobile charge carriers, not immobile ions.
- Option D: Holes are mobile positive charge carriers in the valence band.
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