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Optoelectronic Devices

Last Updated : 04 Feb, 2024
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Optoelectronics is the research, design, and production of a hardware device that transforms electrical energy into light and light into energy using semiconductors. It is the connection between optics and electronics. Optoelectronic devices are special types of semiconductor devices that are able to convert light energy to electrical energy or electrical energy to light energy. Solid crystalline minerals, which are heavier than insulators but lighter than metals, are used to make this device. An optoelectronic device is an electrical gadget that uses light. Numerous optoelectronics applications, including those in the military, telecommunications, automatic access control systems, and medical equipment, use this technology.

Properties of Optoelectronic Devices

  • Such devices have a longer wavelength.
  • They can be easily fabricated.
  • They are cost-effective.
  • They have the size of a manometer.
  • Such devices use high-power light sources.
  • Optoelectronic junction devices are the p-n junction devices in which the carriers are generated by the photons.

Some examples of optoelectronic devices are light-emitting diodes (LED), Solar cells, and Photodiodes. Let us discuss these devices in detail.

Light Emitting Diode (LED)

LED consists of a heavily doped p-n junction diode and is used in forward bias. As we know p side is rich in holes and the n side is rich in electrons. So when current is applied in forward bias, the electrons from the n side of the diode move towards the p side which has holes. The combination of 1 electron and 1 hole results in the release of a photon which is emitted in form of light that we see in LED.

Working of a LED

Working of a LED

Properties of LED

  • The intensity of light emitted by an LED is directly proportional to the magnitude of the current because when more current is applied, more photons will be released and the intensity of light will be more.
  •  The Colour of the emitted light depends upon the band gap (the gap between the conduction band and valence band) of the semiconductor.
  • The reverse breakdown voltage for an LED is low.
  • LED can be formed only using compound semiconductors like GaAs.

Symbol for LED

In physics, LED can be represented using the following symbol:

LED symbol

LED Symbol

Advantages of an LED

  • They are rugged and don’t require any maintenance.
  • They have a fast response time.
  • They emit monochromatic light.
  • They need low operational voltage and consume less power.

Solar Cell

A solar cell is an electrical device that converts light energy to electrical energy. It is a p-n junction semiconductor that generates electricity only when the energy of incident light is greater than its band gap.

Working of Solar Cell

The working of Solar Cells is explained in the article below.

Solar cell


  • When the light (photons) of energy greater than the bandgap of the semiconductor is thrown into the solar cell, the energy of the photons gets transferred to the cell.
  • The energy of the photons is transferred to the electrons in the lower, p-type layer.
  • Due to this energy, the electrons can jump to the upper layer i.e. n-type layer, and then move into the circuit through the metallic conducting strips.
  • Due to the movement of the electrons, the current is produced in the circuit.


It is a device that converts light energy into electric energy. It is used in reverse bias conditions and is generally made of materials such as Silicon, Germanium, and Indium gallium arsenide.

Symbol of Photodiode

In physics, a photodiode can be represented using the following symbol:

Photodiode symbol

Photodiode symbol

The symbol for the photodiode is the same as LED except for the fact that the arrows point inwards which means the photodiode absorbs light energy whereas LED emits light energy.

Working of Photodiode

  • When light having energy greater than the band gap of the semiconductor used in the photodiode is thrown on the photodiode, electron-hole pairs are generated near the depletion region of the p-n junction diode. 
  • These electrons and holes are separated from each other due to the electric field of the depletion region and do not recombine.
  • Electrons move toward the n side and holes move toward the p side of the semiconductor.
  • Due to this movement, an emf is observed.
  • When an external load is connected to a photodiode, the flow of current can be observed in the load.

FAQs on Optoelectronic Devices

Question 1: What are the real-life applications of optoelectronic devices?


LED, LASER, photodiode and solar cell are the real-life applications of optoelectronic devices.

Question 2: Explain the Photovoltaic effect.


The generation of voltage or electric current in a substance as a result of exposure to light is known as the photovoltaic effect, which is a physical and chemical process.

Question 3: Why do we use a photodiode in reverse bias?


A photodiode that is reverse biassed has a wider depletion layer than one that is forward biassed, and it also has a little reverse current (dark current) flowing through it. Under reverse bias, a photodiode greatly increases the amount of incoming light that it converts to current relative to forward bias current.

Question 4: What are the factors on which the color of light emitted by an LED depends?


Light-emitting diodes, sometimes known as LEDs, are semiconductors that transform electrical energy into light energy. The type of semiconductor material affects the hue of the light that is emitting. UV, visible, and infrared are the three wavelengths into which LEDs may be categorised.

Question 5: Differentiate between a photodiode and a solar cell.


A photodiode cell works with an external bias while a solar cell doesn’t work with any external bias.

Question 6: What is the value of the typical operating current for a light-emitting diode?


The value of the typical operating current for a light-emitting diode is approximately 5 to 20 mA.

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