Concept:Donor impurity atoms introduce discrete energy levels (\( E_D \)) just below the conduction band edge \( E_c \) (\( \approx 0.05\text{ eV} \) in Si, \( 0.01\text{ eV} \) in Ge), allowing their fifth valence electrons to be easily excited into the conduction band at room temperature.
Formula:$$\Delta E_{\text{donor}} = E_c - E_D \approx 0.01\text{–}0.05\text{ eV} \ll E_g$$
Solution:- The donor level \( E_D \) lies just below the conduction band edge \( E_c \).
- Thermal energy at room temperature (\( k T \approx 0.026\text{ eV} \)) easily ionizes these donor states, exciting electrons directly into the conduction band.
Why other options are incorrect:- Option B: An energy level just above the valence band (\( E_A \)) describes an acceptor level in P-type semiconductors.
- Option C: The center of the band gap corresponds to the intrinsic Fermi level \( E_i \).
- Option D: Donor states are located in the forbidden gap near the conduction band, not deep in the valence band.
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