P-N JUNCTION DIODE

 P-N JUNCTION DIODE

A p-n junction diode is a semiconductor device created by joining p-type and n-type materials into a single crystal structure. This junction carries majority charge carriers: holes in the p-region and electrons in the n-region.


Biasing of a P-N Junction

Biasing refers to connecting a device to a voltage source. Without a voltage source, no current flows. To allow current to flow through a p-n junction diode, it must be biased using an external voltage source. There are two ways to do this:

(1) Forward biasing
(2) Reverse biasing

(1) Forward Biasing - In forward bias, the p-region of the diode is connected to the positive (+) terminal of the battery, and the n-region is connected to the negative (-) terminal. This allows for easier current flow through the diode.



(2) Reverse Biasing - In reverse bias, the p-region of the diode is connected to the negative (-) terminal of the battery, and the n-region is connected to the positive (+) terminal.

P-N Junction Formation and Depletion Region:

When a p-type and n-type semiconductor are brought into contact, their atoms interact at the boundary. This interaction leads to the formation of a depletion region. In this region, electrons from the n-side diffuse into the p-side, and holes from the p-side diffuse into the n-side. This diffusion results in a region near the junction that is depleted of mobile charge carriers.

Forward Biasing and Current Flow:

Barrier Potential: The depletion region creates a potential barrier that opposes the flow of current.

Overcoming the Barrier: When a forward bias voltage is applied, it reduces the potential barrier. If the applied voltage is greater than the barrier potential, current can flow through the diode.

Current Characteristics: The current-voltage (I-V) characteristic of a forward-biased diode is exponential. The diode exhibits a low resistance in the forward-biased region.

Reverse Biasing and Breakdown:

Increasing the Barrier: When a reverse bias voltage is applied, it increases the potential barrier, making it difficult for current to flow.

Reverse Saturation Current: A small reverse current, known as the reverse saturation current, flows due to minority carriers.

Breakdown: At a high reverse voltage, the diode can experience breakdown. This can be due to avalanche breakdown or Zener breakdown. Avalanche breakdown occurs when the electric field in the depletion region is strong enough to accelerate carriers to high energies, causing them to create additional electron-hole pairs. Zener breakdown occurs when the electric field is so strong that it causes electrons to tunnel through the potential barrier.

Applications of P-N Junction Diodes:

Rectification: Diodes are used to convert AC signals to DC signals.
Switching: Diodes can be used as switches in digital circuits.

Voltage Regulation: Zener diodes are used as voltage regulators to maintain a constant voltage.

Light Emitting Diodes (LEDs): When a forward bias voltage is applied to a special type of p-n junction, it can emit light.
Solar Cells: Solar cells use p-n junctions to convert sunlight into electrical energy.

Additional Considerations:

Diode Models: For circuit analysis, diodes are often modeled using ideal diode models, piecewise linear models, or more complex models.

Temperature Effects: The characteristics of a diode are temperature-dependent. Increasing temperature can increase the reverse saturation current and decrease the forward voltage drop.

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