What is Semiconductor and Its Types , Advantages , Disadvantages , Application

WhatsApp Group Join Now

Telegram Group Join Now

 

A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator. It does not conduct electricity as readily as a conductor, but it can conduct under certain conditions, such as increased temperature or the addition of impurities (doping).

Semiconductors are very important because they are the basic building blocks of modern electronic devices such as diodes, transistors, and integrated circuits.

Atomic Structure of Semiconductor

Semiconductors such as Silicon (Si) and Germanium (Ge) have four valence electrons in their outermost shell. These electrons form covalent bonds with neighbouring atoms.

• Each atom shares electrons with four neighbouring atoms
• This creates a stable crystal structure
• At absolute zero temperature, all electrons are tightly bound

However, when energy is supplied (like heat), some electrons break free and contribute to conduction

Energy Band Theory

In solids, electrons do not exist at a single energy level but in energy bands.

Valence Band (VB)

The valence band contains electrons that are bound to atoms. These electrons cannot move freely and hence do not contribute to conduction.

Conduction Band (CB)

The conduction band contains free electrons that can move easily and conduct electricity.

Forbidden Energy Gap (Band Gap)

The energy gap between the valence band and conduction band is called the forbidden gap.

• In semiconductors → small gap (~1 eV)
• In conductors → no gap
• In insulators → large gap

Because of the small band gap, electrons can easily jump from VB to CB.

Types of Semiconductors

Semiconductors are classified into two main types:

(A) Intrinsic Semiconductor

An intrinsic semiconductor is a pure semiconductor without any impurity.

Explanation:

In intrinsic semiconductors:

• Number of electrons = Number of holes
• Conductivity is low
• Current is due to thermally generated carriers

When the temperature increases:

• Electrons gain energy
• Move from the valence band to the conduction band
• Create electron-hole pairs

Characteristics:

1.     Pure material

2.     Low conductivity

3.     Equal electrons and holes

4.     Conductivity increases with temperature

Example:

Silicon, Germanium

(B) Extrinsic Semiconductor

An extrinsic semiconductor is formed by adding impurities to a pure semiconductor.

This process is called doping.

Purpose of Doping:

• Increase conductivity
• Control electrical properties

Extrinsic semiconductors are of two types:

1. N-type Semiconductor

Formed by doping with pentavalent atoms (5 valence electrons).

Examples: Phosphorus, Arsenic

Working:

• 4 electrons form bonds
• 1 extra electron becomes free

Characteristics:

1.     Majority carriers → Electrons

2.     Minority carriers → Holes

3.     High conductivity

4.     Negative charge carriers dominate

2. P-type Semiconductor

Formed by doping with trivalent atoms (3 valence electrons).

Examples: Boron, Gallium

Working:

• One electron is missing → creates a hole

Characteristics:

1.     Majority carriers → Holes

2.     Minority carriers → Electrons

3.     Conduction due to holes

4.     Positive charge carriers dominate

Charge Carriers

In semiconductors, current flows due to:

(a) Electrons

• Negative charge
• Move to the conduction band

(b) Holes

• Positive charge
• Created when an electron leaves an atom

Both contribute to the current flow.

Doping Process

Doping is the process of adding a small amount of impurity to a semiconductor.

Types:

• Donor impurities → N-type
• Acceptor impurities → P-type

Effects:

1.     Increases conductivity

2.     Controls charge carriers

3.     Improves device performance

Current Mechanism

Drift Current

When an external electric field is applied:

• Electrons move towards the positive terminal
• Holes move towards the negative terminal

This movement produces a drift current.

Diffusion Current

Occurs due to a difference in concentration:

• Electrons move from high to low concentration
• Holes also move similarly

This creates a diffusion current.

Temperature Effect on Semiconductor

• As temperature increases → conductivity increases
• More electrons move to the conduction band
• More electron-hole pairs are generated

This is the opposite of conductors.

Advantages of Semiconductors

1.     Small size

2.     Lightweight

3.     Low power consumption

4.     High efficiency

5.     Reliable

6.     Long life

Applications of Semiconductors

1.     Diodes (Rectification)

2.     Transistors (Amplification)

3.     Integrated Circuits (ICs)

4.     Solar Cells

5.     LEDs

6.     Computers and Mobile devices