The photodiode is a two terminal PN junction device which is operated in reverse bias. It has a small transparent window which allows light to strike the PN junction. The photodiode is a semiconductor device which is used to convert light which is fall on it to current. A photodiode is a semiconductor device with a PN junction and an intrinsic layer between p type and n layer.
It consists of built in lenses and optical filters with small or large surface areas.
The symbol of photodiode is shown in below.
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Construction:
- The basic construction of photodiode is shown in above fig.
- The silicon photodiodes are constructed from single crystal silicon wafers.
- A thin p layer is formed on the front surface of the device of thermal diffusion. N type silicon is a starting material.
- The interface between the p layer and n layer is known as PN junction. To the front of the surface of the device small metal contacts are applied and the entire back is coated with a metal contact.
- Anode is the front contact and the back contact is the cathode.
