Semiconductor Materials

Jul 24, 2024

Semiconductor Materials

Introduction

  • Semiconductor materials are essential for manufacturing electronic devices like transistors, diodes, and integrated circuits.
  • Understanding semiconductor physics and materials is fundamental for learning about basic semiconductor devices.

Why Use Semiconductors in Electronics?

  • Materials are classified based on conductivity: conductors, insulators, and semiconductors.
  • Conductivity measures how easily a material allows the flow of charge, measured in siemens per meter (S/m).

Classification of Materials by Conductivity

  1. Conductors
    • High conductivity.
    • Examples: Silver, copper, gold, aluminum.
    • Avg. conductivity: 10^7 S/m (e.g., copper).
  2. Insulators
    • Poor conductivity.
    • Examples: Wood, glass, Teflon.
    • Avg. conductivity: 10^-14 S/m (e.g., dry wood).
  3. Semiconductors
    • Conductivity between conductors and insulators.
    • Conductivity can be modified by adding impurities (doping).
    • Examples: Silicon, germanium, gallium arsenide.

Silicon: A Key Semiconductor Material

  • Atomic number: 14 (14 protons & 14 electrons).
  • Electron configuration: 4 valence electrons in the outer orbit.
  • Silicon forms a crystal structure by sharing four valence electrons with neighboring atoms, forming covalent bonds.
  • Behavior with Temperature:
    • At temperatures just above 0 K, thermal energy causes atoms to vibrate, breaking some covalent bonds and creating free electrons and holes.
    • At room temperature, the generation and recombination of holes and electrons occur continuously.
    • Equal number of electrons and holes are generated.

Conductivity Mechanism in Semiconductors

  • Current flow in semiconductors is due to electrons and holes (unlike conductors where only electrons contribute).
  • Intrinsic Semiconductors: Pure, without impurities; e.g., pure silicon.
  • Extrinsic Semiconductors: Impurities added to change conductivity; called doping.
  • Types of Extrinsic Semiconductors:
    1. P-Type Semiconductors
      • Trivalent atoms (e.g., aluminum, boron, gallium) with 3 electrons in the outermost orbit added.
      • Creates holes (absence of electrons) which act as positive charge carriers.
      • Trivalent atoms are called acceptor atoms.
    2. N-Type Semiconductors
      • Pentavalent atoms (e.g., arsenic, antimony, phosphorus) with 5 electrons in the outermost orbit added.
      • Creates free electrons which act as negative charge carriers.
      • Pentavalent atoms are called donor atoms.

Majority and Minority Carriers

  • P-Type: Holes (majority), electrons (minority).
  • N-Type: Electrons (majority), holes (minority).
  • Current flow in P-Type is mainly due to holes and in N-Type mainly due to electrons.

Next Steps

  • Upcoming videos will discuss the behavior when combining P-Type and N-Type semiconductors.
  • Q&A and interaction encouraged in the comments section.