PHOTO DIODE

What is a Photo Diode?

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A Photo Diode is an photo detector capable of converting light into either current or voltage depending on the mode of operation. Photo Diodes are designed to opearte in reverse bias condition.
Photo diodes are semiconductor light sensors that can generate a current or voltage when the PN junction is illuminated by light.

When photon of sufficient energy has stricks the diode , then it exites an electron ,there by creating a free electron. This phenomenon is called as inner Photo Electric Effect. If the absorption occurs in the junctions depletion region or, one diffusion length away from it ,these carriers are swept from the junction by the built-in field of the depletion region .Thus holes move towards the cathode and electrons moves towards the anode and a Photo Current is produced. This Photo Current is sum of the dark current and light current , and dark current must be minimized to enhance the senstivity of the device.
Symbol of Photo Diode is Given By

Photo Diodes can be used in three ways .photo voltaic as a solar cell , Reverse- biased as a photo detector and a forward biased LED. Photo Diodes are similar to semiconductor diodes except that they may be exposed to Detect UV rays or X-rays. These Photo Diodes are made up of semi conductor materials like Silicon, Germanium, Indium.

FEATURES OF A PHOTO DIODE:

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Here are the Some of the features of a photo Diode.
1.Excellent Linearity with respect to incident Light.
2.Low Noise.
3.Wide Spectral Response.
4.Mechanically Rugged.
5.Compact and Light Weight.
6.Long Life.

APPLICATIONS:

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1. Photo Diodes are used in consumer electronics such as  CD players, smoke detectors and receivers. 
2. Photo Diodes are used  as light sensors.
3. Photo Diodes are often used for accurate measurement of light intensity in Light industry.
4. Photo Diodes are used in solar cell to generate Electric solar power . 

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And also see: KNOW ABOUT LIGHT EMITING DIODE

LIGHT EMITTING DIODE

What is Light Emitting Diode(LED)?
A Light Emitting Diode(LED) is a semi conductor device that emits visible light when current flows through it. LED is the source of light which converts electrical energy to Light Energy. PN junction diode emits Monochromatic Light , occurring at single wave length.

Light Emitting Diodes are especially PN junction Diodes operated in Forward Bias.

Early LED's can produce Red Light only. But modern LED's can produce different colors including Red,Green,Blue(RGB).We can produce white light also with the help of advancement in the technology. LED requires 1.5-4 V and 10mA to power on. One needs to use a series resistor to prevent overloading.

LED CIRCUIT

In electronics , the basic LED circuit is an electric circuit used to power a Light Emitting Diode(LED).
This simplest circuit consists of a voltage source and a series resistance and an LED. Optionally a switch can be used to open or close the circuit. This switch may be replaced with another component or circuit to from a continuity tester.

HOW DOES LED WORK?

Each time an electron recombines with a positive charge, Electric potential energy is converted into electromagnetic energy. For each recombination of negative and positive charge a quantum of electromagnetic energy is emitted in the form of light with a frequency characteristics of the semi conductor material.
 
 Here are the some of the Advantages of LED over incandescent and fluorescent illuminating devices.
 1.Low Power requirement: Most of the LED's can be operated with Battery supplies.
 2.High Efficiency: Most of the power supplied to the LED has been converted into radiation with    minimum heat production.
3.Long Life: LED's have long life span (often more than 100,000 hours) .If the LED is properly designed then it can be function for decades.

APPLICATIONS :

1.LED's are used in Digital Clocks and display purpose in many applications.
2.They are used in Traffic Controlled systems, Indicator lights and remote controlled devices.
3.As the LED's have long life span they can replace traditional light bulbs in several areas. 

KNOW ABOUT PHOTO DIODE

DIODES

What is a Diode?
Diode is an electronic component with active electrodes ,which allows the flow of current only in one direction.The two electrodes of the diode are Anode(+) and cathode(-).  Diodes are made up of semiconductor materials like silicon, Germanium.

The fundamental property of the diode is to allow the flow of current in only one direction.

How PN junction diode is formed?

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PN junction diode is made from a combination of 2 extrinsic semiconductors such as P-type semiconductor and N-type semiconductor. P-type semiconductor is formed when intrinsic semiconductor is doped with trivalent elements such as Al, Ga and Indium. N-type semiconductor is formed when intrinsic semiconductor is doped with pentavalent impurities such as Phosphorous, Arsenic or Antimony.
Here the joint between P-type and N-type semiconductors is called as PN junction. At the PN junction electrons from the N-type semiconductor will be attracted to the holes of P-type semiconductor. As a result the electrons and holes at the PN junction will disappear forming a layer called "depletion layer". At the same time P-type semiconductor become more negative and N-type semiconductor will become more positive. This results in a potential difference across PN junction.
This potential difference is called as 'Junction voltage or Barrier Voltage'. This junction voltage will prevents the charge carriers from flowing across the depletion region.
Diode can be used in both Forward Bias and Reverse Bias. The polarity of the applied voltage which allows the flow of current is known as 'Forward Bias'. The polarity of the applied voltage which doesn't allows the flow of current to flow is called as 'Reverse Bias'.

Forward Bias:

In Forward Bias positive terminal of the Battery is connected to the P-type material and negative terminal of the Battery is connected to the N-type material of the PN junction Diode. In forward Bias the diode acts as short circuit and start conducting , so that current will pass through Diode .But the diode starts conducting After the 'Cut in voltage or Break over voltage'.Cut in voltage is defined as the minimum voltage below which current is negligible above which the diode starts conducting.Cut in voltage for si is 0.7v and Germanium is 0.3v . 

Reverse Bias:

In Reverse Bias positive terminal of the Battery is connected to the N-type material and negative terminal of the Battery is connected to the p-type material of the PN junction Diode.In reverse Bias the diode acts as open circuit and no current will flow through the diode. 

V-I CHARACTERISTICS OF PN JUNCTION DIODE

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Diodes are mainly used as Rectifiers, Signal limiters, Voltage Regulators ,Switches ,Signal Modulators , Signal Demodulators,Clippers,Clampers.

TYPES OF DIODES: 

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1.LIGHT EMITTING DIODE

2.PHOTO DIODE
  

And also see : TRANSISTORS