Keynotes on Semiconductor Theory

1. Introduction to Semiconductors:

• Definition: Semiconductors are materials with electrical conductivity between conductors (metals) and insulators (ceramics, glass).

• Common Semiconductors: Silicon (Si), Germanium (Ge), and Gallium Arsenide (GaAs).

2. Atomic Structure and Bonding:

• Crystal Lattice: Semiconductors have a crystalline structure where atoms are arranged in a repeating pattern.

• Covalent Bonds: Atoms in a semiconductor crystal are bonded through covalent bonds, sharing electrons to achieve a stable electron configuration.

3. Energy Bands and Band Gap:

• Valence Band and Conduction Band: Electrons in a semiconductor exist in energy bands. The valence band is the highest energy band fully occupied by electrons, while the conduction band is the next higher band where electrons can move freely.

• Band Gap (Eg): The energy difference between the valence band and the conduction band. Semiconductors have a small band gap (e.g., Silicon has Eg ≈ 1.1 eV).

4. Types of Semiconductors:

• Intrinsic Semiconductors: Pure semiconductors without any significant impurities. Electrical conductivity is due to thermally generated electron-hole pairs.

• Extrinsic Semiconductors: Semiconductors doped with impurities to increase conductivity.

  • n-Type: Doped with elements that have more valence electrons (e.g., Phosphorus in Silicon) creating extra electrons.

  • p-Type: Doped with elements that have fewer valence electrons (e.g., Boron in Silicon) creating holes (absence of electrons).

5. Charge Carriers:

• Electrons: Negatively charged particles in the conduction band.

• Holes: Positively charged particles (absence of electrons) in the valence band.

6. Carrier Generation and Recombination:

• Thermal Generation: Electrons gain enough thermal energy to jump from the valence band to the conduction band, creating electron-hole pairs.

• Recombination: Electrons in the conduction band lose energy and fall back into holes in the valence band, releasing energy typically in the form of heat or light.

7. Electrical Conductivity:

• Dependence on Temperature: Conductivity increases with temperature due to increased thermal generation of electron-hole pairs.

• Doping Concentration: Higher doping levels increase the number of free carriers (electrons or holes), enhancing conductivity.

8. Semiconductor Devices:

• Diodes: Allow current to flow in one direction. Constructed from a p-n junction.

• Transistors: Used for amplification and switching. Types include Bipolar Junction Transistors (BJTs) and Field-Effect Transistors (FETs).

• Integrated Circuits (ICs): Complex circuits with many semiconductor devices on a single chip.

9. Applications of Semiconductors:

• Electronics: Fundamental components in computers, smartphones, and other electronic devices.

• Photovoltaics: Solar cells that convert light energy into electrical energy.

• LEDs: Light Emitting Diodes used in displays and lighting.

• Sensors: Devices that detect and respond to various physical inputs like light, temperature, and pressure.

10. Advanced Topics:

• Quantum Mechanics in Semiconductors: Understanding electron behavior at nanoscale using quantum mechanics.

• Semiconductor Fabrication: Techniques like photolithography, doping, and etching used to create semiconductor devices.

• Nanotechnology: Use of nanomaterials and nanostructures to enhance semiconductor properties and applications.