The diode whose internal capacitance varies with the variation of the reverse voltage such type of diode is known as the Varactor diode. Used for storing the charges. The Varactor diode is a voltage dependent semiconductor device works in reverse biased.
The Varactor diode is also called varicap diode or varactor diode or tuning diode.
Construction
- It consists p-type and n-type semiconductor layers sandwiched together, with the n-type layer attached to a mesa structure.
- A gold plated molybdenum stud is connected to n-type layer by the mesa structure and it acts as cathode terminal.
- The p-type layer is connected to another gold plated molybdenum stud acts as anode through a gold wire.
- The entire arrangement is enclosed in a ceramic layer. except for some portion of the molybdenum studs.
- The p-type and n-type layers of are made up of gallium or silicon arsenide depending on the type of application for which it is used.
- Silicon is used for low frequency applications and gallium arsenide is used for high-frequency applications.
- In varactor diode the concentration of impurities is near about the pn junction is very less and it gradually increases as we move towards the layer’s other surface.
Applications
- Harmonic Generators
- Varactor diodes are widely used in frequency modulation or tuning circuits.
- Ultra High Frequency Television sets
- Automatic Frequency Controllers.
- Frequency Multipliers
- Band Pass Filters
- High frequency Radios
