Basics of PN JUNCTION

Understanding Semiconductors and Doping

Semiconductors are materials with electrical conductivity between conductors (metals) and insulators (ceramics), serving as the backbone of modern electronics.

Intrinsic Semiconductors:

• Pure semiconductors without added impurities.

• At room temperature, they have limited free electrons and holes for conduction.

Extrinsic Semiconductors:

• Conductivity is enhanced by adding impurities through doping.

• Pentavalent Impurities (N-type):

  • Elements: Phosphorus (P), Arsenic (As), Antimony (Sb)

  • Valence Electrons: Five; donate one extra electron, increasing conductivity significantly.

  • Majority Carrier: Electrons.

• Trivalent Impurities (P-type):

  • Elements: Boron (B), Aluminum (Al), Gallium (Ga), Indium (In)

  • Valence Electrons: Three; create holes that accept electrons, forming positive charge carriers.

  • Majority Carrier: Holes.

PN Junction:

• Formed by bringing a P-type semiconductor and an N-type semiconductor in contact.

• Diffusion: Charge carriers (electrons and holes) move across the junction, creating a depletion region devoid of free carriers.

• Barrier Potential: The depletion region creates a potential barrier opposing further carrier diffusion.

Applications of PN Junctions:

• Diodes: For rectification, switching, and signal processing.

• Transistors: Essential for digital circuits and amplifiers.

• Solar Cells: Convert sunlight into electricity.

• LEDs: Emit light when current flows through.

Understanding intrinsic and extrinsic semiconductors, doping, and PN junctions is crucial for grasping modern electronic principles.