Concept:Charge transport in semiconductors occurs via two mechanisms: free electron motion in the conduction band and hole motion (electron vacancy shifting) in the valence band.
Formula:$$\vec{J}_{\text{total}} = \vec{J}_n + \vec{J}_p = e(n \mu_n + p \mu_p) \vec{E}$$
Solution:- Conduction band electrons move opposite to the applied electric field vector.
- Valence band electrons move into adjacent vacancies, causing holes to effectively move in the direction of the electric field.
- Because their charges and drift directions are both opposite, both carrier types contribute constructively to total current.
Why other options are incorrect:- Option B: Protons are bound in atomic nuclei and do not drift through the conduction band.
- Option C: Immobile dopant ions are fixed in the lattice, and charge carriers cannot occupy states within the forbidden bandgap.
- Option D: Conduction electrons move through the conduction band, while holes move through the valence band.
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