What is the primary function of a semiconductor diode?

The primary function of a semiconductor diode is to allow electric current to flow predominantly in one direction while blocking it in the opposite direction. This unidirectional conduction property makes it an essential component for converting alternating current (AC) into direct current (DC), a process known as rectification. It also acts as an electronic switch, turning current flow on or off depending on the applied voltage, and is fundamental to various signal processing and power management applications in electronic circuits.

What is the depletion region in a p-n junction, and why is it important?

The depletion region is a thin layer at the p-n junction that is devoid of mobile charge carriers (free electrons and holes). It forms due to the diffusion of majority carriers across the junction, leaving behind immobile charged donor ions on the n-side and acceptor ions on the p-side. This region is crucial because it creates an internal electric field and a potential barrier, which dictates the diode's behavior. The width of this region and the height of the potential barrier determine whether the diode conducts or blocks current under external biasing.

What is the difference between forward bias and reverse bias?

In forward bias, the positive terminal of an external voltage source is connected to the p-type material and the negative terminal to the n-type material. This reduces the potential barrier, allowing a large current to flow. In reverse bias, the connections are opposite: positive to n-type and negative to p-type. This increases the potential barrier, widening the depletion region and effectively blocking the flow of majority carriers, resulting in only a very small reverse saturation current.

What is the cut-in voltage (or knee voltage) of a diode?

The cut-in voltage, also known as the knee voltage or threshold voltage, is the minimum forward bias voltage required across a diode for it to start conducting a significant amount of current. Below this voltage, the current is negligible. For silicon diodes, the cut-in voltage is typically around $0.7, ext{V}$, while for germanium diodes, it's approximately $0.3, ext{V}$. This voltage corresponds to the potential barrier that majority carriers must overcome to cross the p-n junction.

What happens when a diode is subjected to a very high reverse voltage?

When a diode is subjected to a very high reverse voltage, it eventually reaches a point called the breakdown voltage ($V_{BR}$). At this voltage, the reverse current suddenly increases sharply. This breakdown can occur due to Zener breakdown (in heavily doped diodes, where electrons tunnel across the narrow depletion region) or Avalanche breakdown (in lightly doped diodes, where minority carriers gain enough energy to create new electron-hole pairs through collisions). While breakdown can damage a conventional diode if current is not limited, special diodes like Zener diodes are designed to operate safely in this region for voltage regulation.

← ALL TOPICS

Physics

NEXT TOPIC →

Energy Bands in Crystals

Semiconductor Diode

Physics

NEET UG

Version 1Updated 23 Mar 2026

Explore This Topic

Definition Deep Explanation Core Principles NEET Importance Problem Strategy Practice Problems MCQ Practice Quick Revision

A semiconductor diode is fundamentally a two-terminal electronic device formed by joining a p-type semiconductor with an n-type semiconductor, creating a p-n junction. This junction exhibits a unique property of allowing electric current to flow predominantly in one direction (forward bias) while significantly opposing it in the opposite direction (reverse bias), beyond a certain threshold voltage…

Quick Summary

A semiconductor diode is a two-terminal device formed by joining p-type and n-type semiconductor materials, creating a p-n junction. At this junction, a depletion region forms, devoid of mobile charge carriers, and an internal electric field establishes a potential barrier (e.

g., $0.7,\text{V}$ for silicon, $0.3,\text{V}$ for germanium). This barrier dictates the diode's unidirectional current flow property. When forward biased (positive to p-side, negative to n-side), the external voltage reduces the barrier, allowing a large current to flow once the cut-in voltage is surpassed.

The current increases exponentially. When reverse biased (negative to p-side, positive to n-side), the external voltage reinforces the barrier, widening the depletion region and blocking majority carrier flow, resulting in only a tiny reverse saturation current due to minority carriers.

If the reverse voltage exceeds the breakdown voltage, current increases sharply due to Zener or Avalanche breakdown. Diodes are crucial for rectification, switching, and voltage regulation, acting as electronic one-way valves for current.

Vyyuha

Your 6-Month Blueprint, Updated Nightly

AI analyses your progress every night. Wake up to a smarter plan. Every. Single.…

Key Concepts

p-n Junction Formation and Equilibrium

When p-type and n-type materials are brought together, electrons from the n-side diffuse to the p-side, and…

Forward Biasing and I-V Characteristics

In forward bias, an external voltage is applied with the positive terminal to the p-side and negative to the…

Reverse Biasing and Breakdown

In reverse bias, the external voltage is applied with the negative terminal to the p-side and positive to the…

p-n Junction: — Interface of p-type and n-type semiconductors.

Depletion Region: — Region near junction, devoid of mobile carriers, contains immobile ions.

Potential Barrier ($V_B$): — Electric potential across depletion region. Si

approx 0.7,\text{V}

, Ge

approx 0.3,\text{V}

Forward Bias: — Positive to p, negative to n.

V_{ext} > V_B \rightarrow

current flows, depletion region narrows.

Reverse Bias: — Negative to p, positive to n. Depletion region widens, very small reverse saturation current (

I_S

I-V Characteristics: — Exponential current in forward bias after

V_B

. Constant

I_S

in reverse bias until breakdown.

Diode Equation: —

I = I_S left( e^{\frac{V}{eta V_T}} - 1 \right)

Breakdown Voltage ($V_{BR}$): — Reverse voltage where current sharply increases (Zener/Avalanche).

Ideal Diode: —

0,\text{V}

drop in forward, infinite resistance in reverse.

Positive to P, Negative to N = Forward Bias (Current Flows). Reverse is the other way, current Rarely flows.

← ALL TOPICS

Physics

NEXT TOPIC →

Energy Bands in Crystals