A silicon p-n junction with built-in barrier V₀ is studied first unbiased, then with an external voltage V in forward bias and in reverse bias. Which of these statements are correct?

• I. Under forward bias the effective barrier height falls to V₀ − V.
• II. Under reverse bias the depletion region becomes wider.
• III. The small reverse current is due to majority carriers diffusing across the junction.
• IV. With no bias, the diffusion current and drift current across the junction are equal and opposite.