Photodiode works on mainly reverse biased ,and due to reverse biased, minority carriers are used

Photodiode and Current

A photodiode is a semiconductor device that converts light into an electric current. It is made up of a p-n junction, similar to a regular diode, but it is designed to be sensitive to light. When photons of light strike the photodiode, they create electron-hole pairs in the semiconductor material. These electron-hole pairs contribute to the current flow in the device.

Current in a Photodiode

The current in a photodiode is primarily due to the minority carriers. Minority carriers are the charge carriers (electrons or holes) that are present in smaller concentrations compared to the majority carriers in a semiconductor material. In a photodiode, the majority carriers are typically heavily doped and have a much higher concentration compared to the minority carriers.

Generation of Electron-Hole Pairs

When light is incident on the photodiode, photons with sufficient energy can be absorbed by the semiconductor material. This absorption process creates electron-hole pairs, where an electron is excited from the valence band to the conduction band, leaving behind a hole in the valence band. These electron-hole pairs are generated in the depletion region of the p-n junction.

Carrier Separation and Collection

Once generated, the electron-hole pairs are separated by the built-in electric field of the p-n junction. The electric field causes the electrons to move towards the n-side of the junction and the holes to move towards the p-side. This separation of charges creates a photocurrent, as the electrons and holes are now available to contribute to the current flow.

Minority Carrier Contribution

The majority carriers in the photodiode are already present in large numbers due to heavy doping. Therefore, the additional photocurrent is primarily due to the minority carriers, which are generated by the absorption of photons. These minority carriers are swept across the depletion region and contribute to the overall current in the photodiode.

Conclusion

In conclusion, the current in a photodiode is mainly due to the minority carriers. When light is incident on the photodiode, it generates electron-hole pairs, and the separation and collection of these carriers contribute to the photocurrent. The majority carriers in the device, which are already present in high concentrations, do not significantly contribute to the current.