PN junctions and diodes

Which is a characteristic of an avalanche photodiode (APD)?

  1. AIt emits strong light when current flows
  2. BIt uses avalanche multiplication to amplify the photocurrent internally and can detect very weak light
  3. CIt converts AC to DC
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Answer: B. It uses avalanche multiplication to amplify the photocurrent internally and can detect very weak light

An APD is a photodiode biased with a large reverse voltage close to breakdown, so carriers generated by light are multiplied by avalanche multiplication and collected as a large current. Because it can detect very weak light with high sensitivity, it is used in optical communication receivers and LiDAR.

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More PN junctions and diodes questions

  1. In the diode equation I = Is {exp(qV / nkT) − 1}, what current flows when a large reverse voltage is applied (within the range where no breakdown occurs)?
  2. What is the purpose of a diode (flyback diode) connected in parallel with an inductive load such as a relay coil?
  3. In a forward-biased PN junction, which capacitance arises from the storage of injected minority carriers?
  4. How does the depletion width of a one-sided abrupt junction depend on the reverse bias voltage V (when V is much larger than the built-in potential)?
  5. Why are termination structures such as guard rings placed at the edge (periphery) of a high-voltage PN junction?