Introduction to Diodes

                   Introduction to Diodes

• A diode is an electrical device which allows current to flow easily in the circuit. 
• The most common form of diode is semiconductor diode 
• Symbol of a diode  

Introduction to Semiconductor Diodes:-

• Diodes made up of one or more atomic element are called semiconductor diodes. 
• Usually, they are made up of silicon, gallium, aluminum or arsenic. 
• Doping in diodes 

1. This process of injecting impurities is called doping. It creates 2 layers – P type and N type. 
2. In P­type positive electrons are created and in N­type negative electrons are created. 

• Functioning of Semiconductor devices 
  

1. The semiconductor material in this diode is the one that provides the physical properties of the diode. 
2. Materials earlier mentioned like silicon, gallium etc. are injected in the diode with impurities

Types of semiconductor diodes:-

These are the following types of diodes: 

1. Avalanche Diode 
2. Crystal Diode 
3. Light Emitting Diode (LED) 
4. Photodiode 
5. Varactor Diode 
6. Zener Diode 

• Avalanche diode: When the reverse voltage is higher than the breakdown voltage, it conducts in the reverse direction.

• Crystal diode: It consists of a thin sharpened metal wire pressed against a semiconducting material. 

• LED: Light emitting diodes are made up of direct band gap semiconductor which produces wavelength from UV to IR. 
• Photodiode: They are very sensitive to light and are used in solar cells. 
• Varactor diode: These are used as voltage controlled capacitors. 

Characteristics:-

• From the graph shown, it is observed that No current flows when the diode is forward biased. 
• The forward characteristic is non linear A very small leakage current flows in the negative side. 
• p­n junction diode: When p type and n type materials are placed near each other, a junction is formed which allows current to pass through one direction and blocks the other direction. This type is our basic p­n junction diode. 
• Schottky diode: The Schottky diode is a diode with low forward voltage drop and fast switching action. 
• Reverse Recovery Effect: When moving from the conducting to the blocking state, the internal storage charge in the diode has to be discharged. This results in reverse flow of the current. It is called reverse recovery effect. 
• Applications: Diodes are used in constructing logic gates, converting AC to DC, measuring temperature and waveform clipper