14.1 Introduction
Semiconductor electronics deals with materials whose conductivity lies between conductors and insulators. It is the basis for diodes, transistors, and modern electronic devices.
14.2 Classification of Metals, Conductors and Semiconductors
- Conductors: High conductivity (e.g., copper, aluminum)
- Insulators: Very low conductivity (e.g., rubber, glass)
- Semiconductors: Conductivity between conductors and insulators; increases with temperature (e.g., silicon, germanium)
14.3 Intrinsic Semiconductor
- Pure semiconductor material.
- Charge carriers: Electrons and holes generated due to thermal excitation.
- Electron-hole pairs: Responsible for current flow.
- Conductivity (σ) increases with temperature.
14.4 Extrinsic Semiconductor
- Doped semiconductor to increase conductivity.
- Types:
- n-type: Donor impurity (e.g., phosphorus in Si) → excess electrons
- p-type: Acceptor impurity (e.g., boron in Si) → excess holes
14.5 p-n Junction
- Junction between p-type and n-type semiconductors.
- Forms a depletion region with no free charge carriers.
- Barrier potential: Prevents further flow of majority carriers.
- Allows current flow in one direction.
14.6 Semiconductor Diode
- Device made from p-n junction.
- Forward bias: p-side positive, n-side negative → current flows
- Reverse bias: p-side negative, n-side positive → current blocked
- Diode acts as a rectifier, signal limiter, and switch.
14.7 Application of Junction Diode as a Rectifier
- Rectification: Conversion of AC to DC.
- Types of rectifiers:
- Half-wave rectifier: Uses one diode, passes half of AC cycle
- Full-wave rectifier: Uses two or more diodes, passes both AC cycles
- Used in power supplies, battery chargers, and electronic devices.