NEET Notes: Semiconductor Electronics

Introduction to Semiconductor Electronics

Semiconductor electronics deals with materials and devices that control and manipulate electrical signals. This chapter covers the properties of semiconductors, types, and various electronic components such as diodes and transistors that form the backbone of modern electronics.

Classification of Materials Based on Conductivity

Materials are categorized based on their electrical conductivity:

• Conductors: Materials with free electrons that allow easy flow of current (e.g., copper, silver).

• Insulators: Materials with tightly bound electrons, restricting current flow (e.g., rubber, glass).

• Semiconductors: Materials with moderate conductivity, which can be altered using external factors like temperature and doping (e.g., silicon, germanium).

Intrinsic and Extrinsic Semiconductors

Semiconductors are classified into two types:

• Intrinsic Semiconductors: Pure semiconductors without impurities. Conductivity increases with temperature.

• Extrinsic Semiconductors: Doped semiconductors to enhance conductivity, classified into:

  • n-type Semiconductor: Doped with pentavalent elements (e.g., phosphorus), having extra electrons as charge carriers.

  • p-type Semiconductor: Doped with trivalent elements (e.g., boron), creating holes as charge carriers.

p-n Junction and Its Formation

A p-n junction is a fundamental component in semiconductor devices, formed by joining p-type and n-type materials. Key concepts include:

• Depletion Region: A charge-free zone at the junction due to the recombination of electrons and holes.

• Barrier Potential: A small voltage across the depletion region that prevents further charge carrier movement.

Biasing of p-n Junction

A p-n junction diode operates under different biasing conditions:

• Forward Bias: External voltage reduces the barrier potential, allowing current to flow.

• Reverse Bias: External voltage increases the barrier potential, preventing current flow except for a small leakage current.

Semiconductor Diodes and Their Applications

A diode is a device that allows current to flow in one direction. Types of semiconductor diodes include:

• Light Emitting Diode (LED): Converts electrical energy into light, widely used in indicators and displays.

• Photodiode: Generates current when exposed to light, used in sensors.

• Zener Diode: Operates in reverse bias and maintains a constant voltage, used in voltage regulation.

Transistors and Their Applications

A transistor is a three-terminal semiconductor device used for amplification and switching. It has two main types:

• Bipolar Junction Transistor (BJT):

  • Consists of Emitter, Base, and Collector.

  • Works in three configurations: Common Base (CB), Common Emitter (CE), and Common Collector (CC).

  • Used in amplifiers, oscillators, and logic circuits.

• Field Effect Transistor (FET):

  • Works on voltage-controlled principles.

  • Includes Junction FET (JFET) and Metal-Oxide-Semiconductor FET (MOSFET).

  • Used in microprocessors and digital circuits.

Logic Gates and Digital Electronics

Logic gates are the basic building blocks of digital circuits, performing logical operations:

• Basic Gates: AND, OR, NOT.

• Universal Gates: NAND, NOR (can implement any Boolean function).

• Exclusive Gates: XOR, XNOR (used in parity checking and data processing).

Applications of Semiconductor Electronics

Semiconductor devices play a crucial role in:

• Communication Systems – Mobile phones, satellite communication.

• Computers and Microprocessors – Used in integrated circuits (ICs).

• Medical Equipment – MRI scanners, pacemakers.

• Power Electronics – Solar cells, voltage regulators.

Conclusion

Semiconductor electronics revolutionized modern technology by enabling the development of compact, efficient, and high-speed electronic devices. Understanding the principles of semiconductors is crucial for NEET aspirants as it forms the foundation for various real-world applications in engineering and medical technology.