Question

Write notes on the photodiode.

Answer 1

           Circuit symbol

Schematic view of photodiode

1. Photodiode is a p-n junction diode that converts an optical signal into electric current.
2. It works in reverse bias.
3. It consists of an F p-n junction semiconductor made of photosensitive material kept safely inside a plastic case.
4. It has a small transparent window to allow light.
5. When photon (hv) strikes depletion region of diode some valence band electrons elevated to conduction band. In turn, holes are developed in the valence band. This creates electron-hole pair.
6. Amount of electron-hole pairs generated depends on the intensity of light.
7. These electrons and holes swept across the junction by the electric field. Thus holes move to the n side, electrons to the p side.
8. When an external circuit is made, electrons flow through an external circuit and constitute the photocurrent.

Applications:
Alarm system, count items in the conveyer belt, photoconductors, CD players, smoke detectors, detectors for computed tomography, etc.