Notes on P-N Junction Diode

Introduction

• Presenter: Ami Patel
• Topic: P-N Junction Diode
• Overview: Discusses types of materials, semiconductor types, basic circuit elements, and characteristics of P-N junction diode.

Types of Materials

• Three types:
  • Metal
  • Semiconductor
  • Insulator
• Energy Band Diagram:
  • Conduction Band: Contains free electrons.
  • Valence Band: Electrons bonded in covalent bonds.
  • Metals: Overlapping conduction and valence bands.
  • Semiconductors: Small gap between conduction and valence bands.
  • Insulators: Large gap between conduction and valence bands.
• Semiconductor Properties:
  • Conductivity can be altered by external voltage, heat, or light.

Types of Semiconductor Materials

• Intrinsic Semiconductor:
  • Chemically pure, poor conductivity.
  • Equal number of electrons and holes; current due to thermal agitation.
• Extrinsic Semiconductor:
  • Formed by adding impurities (trivalent or pentavalent) to intrinsic semiconductors (doping).
  • Unequal number of electrons and holes.

Basic Circuit Elements

• Resistor:
  • Opposes current flow; used to control current.
• Capacitor:
  • Stores electric charge.
• Inductor:
  • Stores energy in a magnetic field when current flows through it.

P-N Junction Diode

• Definition:
  • Allows current flow in one direction; blocks current in the opposite direction.
• Construction:
  • Formed by joining P-type and N-type materials.
  • Anode (P-side) and Cathode (N-side) terminals.
• Symbol:
  • Triangular shape with flat side indicating the anode.

Formation of P-N Junction

• Junction Formation:
  • Electrons (N-side) and holes (P-side) move across the junction (Diffusion).
  • Positive charge builds on N-side, negative charge builds on P-side.
  • Creates a Depletion Region with no free carriers.

Biasing of P-N Junction Diode

• Definition of Bias:
  • Application of external DC voltage across the diode.
• Forward Bias:
  • Anode connected to positive terminal, cathode to negative.
  • Current flows when forward voltage overcomes potential barrier (cutting voltage).
  • Cutting voltage: 0.3V for Germanium; 0.6-0.7V for Silicon.
• Reverse Bias:
  • Anode connected to negative terminal, cathode to positive.
  • Majority charge carriers move away from the junction, increasing the depletion region width.
  • Reverse saturation current flows, typically in microamperes.

Current-Voltage (V-I) Characteristics of P-N Junction Diode

• Forward Bias Characteristics:
  • No current until cutting voltage is reached, then current increases significantly.
• Reverse Bias Characteristics:
  • Negative voltage and current; reverse saturation current remains low until breakdown voltage is reached, beyond which the diode can be damaged.

Key Terms

• Cutting Voltage (Knee Voltage):
  • Minimum forward voltage for current to flow.
• Breakdown Voltage:
  • Reverse voltage at which breakdown occurs.
• Depletion Region:
  • Region with immobile ions and no free carriers near the junction.

Conclusion

• Summary of key concepts regarding P-N junction diodes and their characteristics.
• Encouragement to stay connected for more sessions.