Concept:Even in complete darkness, thermal energy in the crystal lattice generates electron-hole pairs in and near the depletion layer. The reverse-bias electric field sweeps these carriers across the junction, creating a small leakage current known as the dark current.
Formula:$$I_{\text{dark}} = I_0 = q A \left( \frac{D_n n_{p0}}{L_n} + \frac{D_p p_{n0}}{L_p} \right) + \frac{q A n_i W}{2 \tau_0}$$
Solution:- Thermal vibrations break covalent bonds at room temperature, generating electron-hole pairs.
- The electric field in the depletion layer separates these carriers before they recombine, producing a steady background current (dark current).
Why other options are incorrect:- Option A: Ambient radio waves have photon energies far below the semiconductor bandgap.
- Option B: Reverse bias prevents majority carrier diffusion.
- Option C: Standard semiconductor dopants are stable non-radioactive isotopes.
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