How does a Diode Work? A Simple Explanation | How Diodes Work | Electrical4U

Summary

This video explains the working principles of a PN junction diode, covering the structure of n-type and p-type semiconductors and their behavior when combined. It highlights the formation of the depletion region, the concept of barrier potential, and the effects of forward and reverse biasing. When forward biased, the diode allows current to flow once the applied voltage exceeds the barrier potential, while reverse biasing widens the depletion region and blocks current flow. The video also discusses the concept of minority carriers and reverse saturation current. It offers a clear, concise overview of how diodes function in electronic circuits.

Takeaways

• 😀 n-type semiconductors have free electrons as the majority carriers, while p-type semiconductors have holes as the majority carriers.
• 😀 A PN Junction diode is formed by joining n-type and p-type materials, leading to the creation of a depletion region at the junction.
• 😀 The depletion region is a zone devoid of free charge carriers, created by the recombination of free electrons and holes.
• 😀 The electric field formed by the uncovered donor and acceptor ions in the depletion region creates a barrier potential that opposes further carrier movement.
• 😀 In forward bias, the positive terminal is connected to the p-type side, and the negative terminal to the n-type side, reducing the barrier potential.
• 😀 If the applied forward voltage exceeds the barrier potential (0.7V for silicon, 0.3V for germanium), the diode allows current to flow.
• 😀 In reverse bias, the positive terminal is connected to the n-type side and the negative terminal to the p-type side, increasing the depletion region and preventing current flow.
• 😀 Reverse bias does not allow current flow under normal conditions, but a tiny reverse saturation current flows due to minority charge carriers.
• 😀 The reverse saturation current is minimal and results from thermally generated holes in n-type semiconductors and free electrons in p-type semiconductors.
• 😀 The diode blocks current when reverse biased and conducts current when forward biased, depending on the applied voltage exceeding the barrier potential.

Q & A

What is the main difference between N-type and P-type semiconductors?

In an N-type semiconductor, the majority carriers are free electrons, whereas in a P-type semiconductor, the majority carriers are holes.

What is the role of thermal excitation in the formation of electron-hole pairs?

Thermal excitation causes the generation of electron-hole pairs in both N-type and P-type semiconductors, where free electrons and holes are created due to the energy provided by heat.

What happens when N-type and P-type materials are joined together?

When N-type and P-type materials are joined, free electrons from the N-type side recombine with holes from the P-type side, forming a depletion region at the junction where no free carriers exist.

What is the depletion region in a diode?

The depletion region is the area at the junction of N-type and P-type materials where free electrons and holes recombine, leaving behind immobile ions that create an electric field, forming a barrier potential.

What is the barrier potential in a PN junction?

The barrier potential is the voltage created across the junction due to the electrostatic force from the immobile donor and acceptor ions in the depletion region. This voltage opposes the flow of carriers across the junction.

What happens when a diode is forward biased?

In forward bias, the positive terminal of the voltage source is connected to the P-type side and the negative terminal to the N-type side. This reduces the barrier potential, allowing current to flow through the diode when the applied voltage exceeds the barrier potential.

What is the threshold voltage for silicon and germanium diodes in forward bias?

For a silicon diode, the threshold voltage (or forward bias voltage) is approximately 0.7V, while for a germanium diode, it is around 0.3V.

What happens when a diode is reverse biased?

In reverse bias, the positive terminal is connected to the N-type side and the negative terminal to the P-type side, causing the depletion region to widen, preventing the flow of current.

What is reverse saturation current in a diode?

Reverse saturation current is a small current that flows through the diode even when it is reverse biased, due to thermally generated minority carriers (free electrons in P-type and holes in N-type).

Why does a diode block current in reverse bias, except for reverse saturation current?

A diode blocks current in reverse bias because the widening depletion region prevents majority carriers from crossing the junction. However, a tiny current flows due to minority carriers, which is called reverse saturation current.