Semiconductor Electronics: Materials, Devices and Simple Circuits

Photodiodes Applications

A photodiode refers to a PN-junction diode that consumes light energy for producing an electric current. We also refer to them as a photo-detector, a light detector, and a photo-sensor. They have been designed to work in reverse bias conditions. The typical photodiode materials are Silicon, Germanium, and Indium gallium arsenide. In this article, we will study in detail photodiodes applications.

photodiodes applications

Introduction to Photodiodes Applications

A photodiode subjects photons in the form of light which impacts the production of electron-hole pairs. If the energy of the falling photons (hv) is bigger than the energy gap (Eg) of the semiconductor material, electron-hole pairs produce near the depletion region of the diode.

The electron-hole pairs form separate from each other before recombining because of the electric field of the junction. The direction of the electric field in the diode is what forces the electrons to move towards the n – side and thus, the holes move towards the p-side.

Due to the increase in the number of electrons on the n – side, and holes on the p-side, one can observe a rise in the electromotive force. Now, when an external load connects to the system, we observe a current flow through it.

In other words, the more the electromotive force creates, the greater will be the current flow. The magnitude of the electromotive force produces is dependent directly upon the intensity of the incident light.

This consequence of the proportional change in photocurrent with the change in light intensity can be simply detected by applying a reverse bias. Moreover, as photodiodes produce current flow directly depending upon the light intensity they receive, we can use them as photodetectors for detecting optical signals.

Similarly, we can also use built-in lenses and optical filters for enhancing the power and productivity of a photodiode.

Symbol of Photodiode

This is the symbol of the photodiode:
photodiodes applications

This symbol is similar to that of an LED, but you will notice that the arrow her is pointing inwards.

Applications of Photodiode

We will not study the applications of photodiodes:

  1. We make use of photodiodes in simple day-to-day applications. The reason why we use them so prominently is because of their linear response of photodiode to light illumination.
  2. They come into use in the detection circuits.
  3. Along with the help of optocouplers, photodiodes offer electric isolation. When two isolated circuits illuminate by light, optocouplers come in use to couple the circuit optically. Moreover, optocouplers are faster when we compare them to conventional devices.
  4. They are used for the exact measurement of the intensity of light in science and industry.
  5. We also use them in safety electronics like fire and smoke detectors.
  6. Photodiodes also come into use in character recognition circuits.
  7. They also come into use in several medical applications. We use them in instruments that analyse samples, detectors for computed tomography and also in blood gas monitors.
  8. We use them in solar cell panels.
  9. They also come into use in logic circuits.
  10. Finally, they are faster and more complex than normal PN junction diode and we use them frequently for lighting regulation and optical communication.

FAQ on Photodiodes Applications

Question 1: Why are photodiodes used in reverse bias?

Answer 1: It is reverse biased for operating in the photoconductive mode. As the photodiode is in reverse bias the width of the depletion layer keeps increasing. Thus, it reduces the junction capacitance and in that way the response time. In effect, the reverse bias causes faster response times for the photodiode.

Question 2: What are photodiodes and mention its application?

Answer 2: We use photodiodes in safety electronics like fire and smoke detectors. We also use them in many medical applications. Moreover, we use them in instruments that analyse samples, detectors for computed tomography. Similarly, we also use them in blood gas monitors and in solar cell panels.

Question 3: What are the advantages of a photodiode?

Answer 3: There are many advantages of a photodiode. Some of them are that it is linear and has low resistance. Further, it has a very good spectral response. Moreover, its frequency response is also better in addition to having a low dark current. It is the fastest photodetector and has a long life in addition to having low noise.

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