Q4. Of what order is the thickness of the depletion region of a p-n junction?
About one-tenth of a micrometre, 10−7 m (NCERT page 333). Strictly, the width depends on the doping and the bias (reasoned).
Q5. An electron diffuses from the n-side to the p-side. What does it leave behind, and on which side?
An ionised donor, a fixed positive charge, on the n-side of the junction (NCERT page 333).
Q6. Assertion: in an unbiased p-n junction the n-side is at a higher potential than the p-side. Reason: the n-side has lost electrons by diffusion. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: the fixed donor ions left on the n-side make it positive relative to the p-side (NCERT page 334).
Q7. A junction has a barrier potential of 0.3 V across a depletion region 0.1 μm wide. Estimate the average field in it.
E ≈ V0/W = 0.3/10−7 = 3 × 106 V m−1 (beyond the NCERT text; width from NCERT page 333).
Q8. Why is the region near the junction called the depletion region?
The electrons and holes that crossed the junction at first have depleted the region of its free charges, leaving only the fixed donor and acceptor ions (NCERT page 333). Strictly, a few mobile carriers remain; the depletion approximation neglects them (reasoned).