Image sensors and optical devices

When the light falling on a reverse-biased photodiode becomes stronger, how does the current (photocurrent) change?

  1. AIt does not change
  2. BIt increases roughly in proportion to the light intensity
  3. CIt decreases
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Answer: B. It increases roughly in proportion to the light intensity

In a photodiode, absorbed photons create electron-hole pairs that are separated by the field in the depletion layer and become current. Stronger light means more photons, so the photocurrent increases roughly in proportion to the light intensity. This good linearity is one reason photodiodes are used as light sensors.

  • A. The current changes with the light intensity.
  • B. Correct. The photocurrent is roughly proportional to the light intensity.
  • C. Stronger light generates more carriers.
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