Discussion
The potential barrier in a pn-junction is formed after stabilizing the carrier transport. Under this condition :
Answer: C
At equilibrium, drift current = diffusion current.
When a pn junction forms, holes and electrons diffuse across it because of the concentration difference, leaving behind uncovered ions that make up the depletion region. Those ions set up an electric field, which drives a drift current in the opposite direction. Diffusion continues only until the field, and so the potential barrier, has grown just enough for the drift current to cancel the diffusion current exactly. That balance is what 'stabilized' means, and it is why no net current flows through an unbiased junction.
If drift exceeded diffusion, or vice versa, a net current would flow with no external source, which cannot happen in equilibrium.
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