PN junctions and diodes
How does the breakdown voltage of a PN junction generally change when the impurity concentration on one side is lowered?
- AIt does not depend on impurity concentration
- BIt becomes lower
- CIt becomes higher
Show answer and explanation
Answer: C. It becomes higher
With a lower impurity concentration, the depletion layer extends further at the same voltage and the field in the junction is weaker. A higher voltage is then needed to reach the critical field for avalanche breakdown, so the breakdown voltage rises. This is why high-voltage power devices use lightly doped drift layers.
- A. The breakdown voltage depends strongly on impurity concentration.
- B. Heavier doping lowers the breakdown voltage; lighter doping raises it.
- C. Correct. The depletion layer widens and the field weakens, so the breakdown voltage rises.