PN junctions and diodes

Which property does a variable-capacitance (varactor) diode use?

  1. AEmitting light with forward current
  2. BResistance changing with temperature
  3. CJunction capacitance changing with reverse bias voltage
Show answer and explanation

Answer: C. Junction capacitance changing with reverse bias voltage

When reverse bias is applied to a PN junction, the depletion width changes with voltage and so does the junction capacitance. A varactor diode uses this to control capacitance with voltage. It is used in radio and TV tuners and in voltage-controlled oscillators (VCOs).

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More PN junctions and diodes questions

  1. In a PN junction where the p side is far more heavily doped than the n side (a p+n junction), how does the depletion layer spread?
  2. Why does a reverse current flow briefly (a reverse recovery time exists) when a PN junction diode is switched from forward to reverse?
  3. How does the built-in (diffusion) potential of a PN junction relate to the doping on each side?
  4. Which correctly describes the mechanism of avalanche breakdown?
  5. In a very heavily doped PN junction, what is the main mechanism of breakdown at low reverse voltage?