What is Photo Diode? – Working, Characteristics, Applications | New Topic [2024]

In this note, we are going to learn a topic called “What is Photo Diode?“, also its working principle, VI Characteristics, Applications as well. Welcome to Poly Notes Hub, a leading destination for polytechnic notes or engineering notes.

Author Name: Arun Paul.

What is Photo Diode?

A Photodiode is a semiconductor device that converts light to electrical current. When light photons impact the photodiode, electron-hole pairs form in the semiconductor material, causing current to flow. Photodiodes are widely utilized in a variety of applications, including light detection, optical communication, and sensing. They are sensitive to various wavelengths of light depending on the material used and can be found in devices such as cameras, barcode readers, and solar cells.

what is photo diode - poly notes hub
Photo Diode Symbol
photo diode symbol - poly notes hub

Internal Structure of Photo Diode

internal structure of photo diode - poly notes hub
  • Semiconductor Material: Photodiodes are commonly built of semiconductors like silicon, germanium, or gallium arsenide. When exposed to light, these materials produce electron-hole pairs.
  • P-N Junction: A p-n junction is produced by doping the photodiode’s semiconductor material. The semiconductor’s p-type (positively doped) and n-type (negatively doped) regions are divided by this junction.
  • Metal Contacts: The p-type and n-type sections of the photodiode have metal connections linked to them, which enable the connecting of external circuitry.
  • Optical Window: To prevent damage and let light in, the semiconductor material in certain photodiodes is covered by an optical window.

Photo Diode Working Principle

photo diode working principle - poly notes hub

A photodiode’s operating principle is based on the photovoltaic effect, which occurs when light photons are absorbed and create electron-hole pairs in semiconductor material. When photons with sufficient energy reach the photodiode’s semiconductor junction, electrons are excited from the valence band to the conduction band, resulting in electron-hole pairs.

This process causes current to flow through the photodiode, which may be measured externally. The current generated is proportional to the intensity of the incident light. Photodiodes are frequently employed in reverse bias configurations, which apply a voltage across the diode to increase its sensitivity and response time.

Photo Diode Characteristics

vi characteristics of photo diode - poly notes hub
Below shows the VI characteristics of Photo Diode –
  • In the dark, the photodiode functions similarly to a reverse-biased diode, with just a little leakage current.
  • The photocurrent created increases in proportion to the intensity of the incident light.
  • Within a specific range, VI characteristics usually exhibit a linear connection between photocurrent and applied reverse bias voltage.
  • At greater reverse bias voltages, the photodiode may reach saturation with minor increases in photocurrent.
  • Overall, VI characteristics show how the photodiode converts light energy into electrical current and how it performs under various settings.

Photo Diode Applications

Below we listed some important applications of photo diode –
  1. Used in light meters, ambient light sensors, and display brightness control systems.
  2. In fiber optic communication systems, optical signals are received and converted to electrical signals.
  3. Used in flame sensors to detect the presence of flames using emitted light.
  4. Pulse oximeters measure blood oxygen levels, while photoplethysmography measures blood flow.
  5. Devices used to detect infrared signals in consumer gadgets.
  6. Used in Security systems include motion detectors, surveillance cameras, and laser-based security systems.
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