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Opto Electronic Devices [Complete Guide]

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  • Optoelectronics is the communication of optics and electronics which involves the study, design and manufacturing of hardware device which converts electrical energy into light and light into energy through semiconductors.
  • Made up of semiconductor materials.
  • Used in Military services, telecommunications,automatic access control systems and medical equipments.

Types of Optoelectronic devices

  • LED
  • Photo diode
  • Photo transistor

Light Emitting Diode(LED)

  • PN- Junction opto-semiconductor
  • Emits monochromatic light when operated in forward bais condition
  • Converts electrical energy to light energy


  • When sufficient voltage is applied to the leads of the LED, electrons move in one direction across the junction between the p and n regions.
  • The electrons recombine with the holes within the device.
  • Release energy in the form of photons.
  • This effect is called electroluminescence.

Advantages of LED

  • Consumes less power
  • Produces less heat
  • Last longer than incandescent lamps

Disadvantages of LED

  • Costly
  • Temperature sensitivity
  • Voltage sensitivity

Application of LED

  • Mobile applications
  • LED signals
  • Automative uses
  • Illumination
  • Indicators

Photo Diode

  • Light sensor made up of semiconductor materials
  • When light falls on the junction, voltage or current is generated
  • PN- Junction diode, operated in reverse bais
  • When a photon(light) strikes a semiconductor, electron- hole pairs are generated through band-band optical absorption
  • Electric field is produced when the electron diffuse into the junction
  • This electric field across the depletion region is equal to the negative voltage across the unbaised diode. This is known as inner photoelectric effect


  • Optical energy(light) is converted to electrical energy(current/voltage) through optical receivers.
  • Refered to as O/E Converter.
  • Photodector is the fundamental element of optical receivers.

Advantages of Photo diode

  • Cost efficient
  • Light weight and compact in size
  • Wide spectral response
  • Quick responce when exposed to light

Disadvantages of Photo diode

  • Low illumination levels due to reverse current
  • Temperature dependent

Applications of photodiode

  • Fire and smoke detectors
  • Photo sensors in camera
  • Dectectors for computed tomography
  • Blood gas monitors

Photo transistor

  • Similar to bipolar junction transistor(BJT)
  • Only difference is that base current is produced and controlled by light except voltage source
  • Converts light energy to electrical signal
  • Light sensitive
  • Have collector, base and emitter


  • Light sensitive collector base pn junction controls current flow between emitter and collector
  • Resistance decreases as intensity increases, creating more emitter-base current
  • The small base current controls the larger emitter-collector current

Advantages of Photo transistor

  • More sensitive than photodiodes of comparable size
  • Produce higher current than photodiodes
  • Fast response, compact enough to fit onto single integrated computer chip

Disadvantages of Photo Transistor

  • Silicon phototransistors cannot handle voltages above 1000V.
  • More susceptible to electricity surges

Applications of Photo Transistor

  • Lighting control(Roads,highways,etc.)
  • IR Detectors
  • Counting systems
  • Security systems
Opto Electronic Devices [Complete Guide]
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