Special Purpose P-N Junction Diodes - Practice Questions & MCQ

Devices in which carriers are generated by photons are called optoelectronic devices.

The following are important examples of optoelectronic devices.

1. Photodiodes to detect optical signals
2. Light Emitting Diodes (LEDs)
3. Solar cells

• Photodiode-

A photodiode is a p-n junction that consumes light energy to generate electric current. It is operated under reverse bias.

Reverse bias means that the p-side of the photodiode is connected to the negative terminal of the battery and the n-side is connected to the positive terminal of the battery.

It is also sometimes referred to as a photo-detector, photo-sensor, or light detector.

Suppose an optical photon of frequency    is incident on a semiconductor, such that its energy is greater than the bandgap of the semiconductor (i.e.$h \nu>E_g$). This photon will excite an electron from the valence band to the conduction band leaving a vacancy or hole in the valence band. This increases the conductivity of the semiconductor.

And by measuring the change in the conductance (or resistance) of the semiconductor, one can measure the intensity of the optical signal. Thus photodiode can be used as a photodetector to detect optical signals.