Name: p-n junction diode under bias
Uploaded: 2025-05-22T09:06:15.000Z
Duration: 1 min 16 s
Channel: JoVE

The p-n junction within an LED requires external biasing to produce light.
Forward biasing involves applying a voltage across the p-n junction with the battery&#39;s positive terminal connected to the p-side and the negative terminal to the n-side. The applied voltage opposes the junction potential, reducing the barrier width.
This reduced barrier width enables current flow by increasing majority carrier diffusion. The diffusion current is higher than the drift current, and the net current flows in the forward direction from p to n.
During diffusion, the recombination of electrons and holes in the junction region emits photons, making the LED glow.
In reverse biasing, the battery&#39;s positive terminal is connected to the n-side and negative to the p-side.
This prevents the LED from glowing as the applied potential adds to the junction potential, resulting in an increased barrier width and a decreased majority carrier diffusion.
The net current is the small drift current obtained due to minority carriers.
If the reverse bias voltage exceeds a certain threshold, junction breakdown occurs, resulting in a large current flow.

biasing of p-n junction

The operation of a p-n junction diode involves various biasing conditions, including forward bias, reverse bias, and equilibrium.
In equilibrium, no external voltage is applied across the p-n junction. The depletion region is formed at the junction interface due to the diffusion of carriers, which leaves behind charged dopants, acceptors on the p-side, and donors on the n-side. These immobile charges create an electric field that prevents further diffusion of carriers. The related energy band diagram shows that the Fermi levels on both sides are aligned, indicating equilibrium. The built-in potential across the junction prevents the net flow of carriers across the junction.
When the diode is forward biased the applied voltage reduces the barrier potential and narrows the width of the depletion region. As a result, carriers can easily cross the junction, and the corresponding band diagram shows the energy bands bending upwards, indicating the reduction of the barrier potential. The current across the diode under forward bias increases exponentially with the applied voltage.
In reverse bias, the external voltage is applied in the opposite direction, widening the depletion region, increasing the barrier potential, making it difficult for carriers to cross the junction, and reducing the current flow to a very small reverse saturation current. The energy band diagram for reverse bias shows the bands bending downwards, indicating increased barrier potential. The current in reverse bias is a small constant value. It is close to the saturation current but with the opposite sign, reflecting the minor flow of carriers due to thermal generation within the depletion region.

Biasing of P-N Junction

The operation of a p-n junction diode involves various biasing conditions, including forward bias, reverse bias, and equilibrium.
In equilibrium, no ...

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Electrical Engineering

Unit 1

Basics of Semiconductors

KEY TERMS AND CONCEPTS

p-n junction diode under bias

P-N junction diodes change behavior under equilibrium, forward bias, and reverse bias. In equilibrium, no external voltage is applied across the junction. Carriers diffuse at the boundary and leave behind charged dopants. Acceptors remain on the p-side, and donors remain on the n-side. These fixed charges form a depletion region and an electric field that blocks further diffusion.

The band diagram at equilibrium shows the Fermi levels on both sides aligned. That alignment means the junction is in balance. A built-in potential also exists across the junction. This potential prevents a net flow of carriers from one side to the other.

When the diode is forward biased, the applied voltage lowers the barrier potential. It also narrows the depletion region. Carriers can then cross the junction more easily. The band diagram shows the energy bands bending upward, which matches the reduced barrier.

Forward bias also causes the current to rise quickly as the applied voltage increases. The current increases exponentially with voltage. In reverse bias, the external voltage is applied in the opposite direction. The depletion region widens, the barrier potential increases, and carrier flow becomes very small.

The reverse-bias band diagram shows the energy bands bending downward. This change reflects the higher barrier potential. The current falls to a small reverse saturation current. It stays close to that saturation value and has the opposite sign, because only a minor carrier flow remains from thermal generation within the depletion region.

P-N Junction Diode Under Bias

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A p-n junction forms when p-type and n-type semiconductor materials are joined together. At the boundary, holes from the p-side and electrons from the n-side diffuse into the opposite side because of the concentration gradient. This movement leaves a region with no free charge carriers near the junction, called the depletion region. The charge density in the depletion region can be described on the n-side and p-side using the donor and acceptor doping concentrations, ND and NA. The fixed...

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Explore equilibrium, forward bias, and reverse bias in a p-n junction diode, including depletion region changes, band diagrams, and current flow.

P-N Junction Diode Under Bias | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

P-N Junction Diode Under Bias

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