What Are Semiconductors?

Semiconductors are materials that have electrical conductivity between conductors (like metals) and insulators (like glass). They are the foundation of modern electronics, enabling the creation of devices like computers, smartphones, and solar panels.

  • Common Semiconductor Material: Silicon (Si)
  • Other Examples: Germanium (Ge), Gallium Arsenide (GaAs)

Structure of Semiconductors

Atoms in a semiconductor are arranged in a crystal lattice. Each silicon atom shares electrons with four neighbors, forming strong covalent bonds.

Silicon Crystal Lattice

Figure: Silicon crystal lattice structure.

Types of Semiconductors

1. Intrinsic Semiconductors

  • Pure form, e.g., pure silicon.
  • Conductivity is low.

2. Extrinsic Semiconductors

  • Doped with impurities to increase conductivity.
  • n-type: Added atoms have extra electrons (e.g., Phosphorus in Silicon).
  • p-type: Added atoms have fewer electrons (e.g., Boron in Silicon).

Doping in Semiconductors

Figure: Doping creates n-type and p-type semiconductors.

How Semiconductors Work

  • At low temperatures: Electrons are tightly bound; little conductivity.
  • At higher temperatures or with doping: Electrons can move, allowing current to flow.

Band Theory

  • Valence Band: Electrons are bound.
  • Conduction Band: Electrons are free to move.
  • Band Gap: Energy difference between bands; smaller in semiconductors than in insulators.

Applications of Semiconductors

  • Transistors: Switches for electronic signals.
  • Diodes: Allow current in one direction.
  • Solar Cells: Convert sunlight to electricity.
  • LEDs: Emit light when current passes through.

Case Studies

1. Microprocessor Revolution

Modern computers use billions of transistors made from silicon. The Intel 4004 (1971) had 2,300 transistors; today’s chips have over 50 billion.

2. Solar Energy Breakthroughs

Recent advances in perovskite semiconductors have increased solar panel efficiency. In 2022, researchers at NREL developed perovskite cells with over 25% efficiency (NREL News, 2022).

3. Medical Devices

Semiconductors power MRI machines, pacemakers, and wearable health monitors, making healthcare more precise and accessible.

Surprising Facts

  1. Quantum Weirdness: At nanoscales, semiconductor behavior is governed by quantum mechanics, leading to phenomena like tunneling.
  2. Brain vs. Chips: The human brain has more connections (synapses) than there are stars in the Milky Way—over 100 trillion!
  3. Self-Healing Materials: Some new semiconductors can “heal” microscopic cracks, improving device lifespan (Science Advances, 2021).

Ethical Issues

  • Resource Extraction: Mining silicon and rare elements can harm environments and communities.
  • E-Waste: Discarded semiconductor devices contribute to global electronic waste.
  • Privacy: Semiconductor-powered devices (phones, cameras) raise concerns about surveillance and data security.

Recent Research

A 2023 study in Nature Electronics describes ultra-thin, flexible semiconductors for wearable tech, enabling new medical and fitness applications (Nature Electronics, 2023).

Further Reading

Summary Table

Property Conductor Semiconductor Insulator
Conductivity High Medium Low
Band Gap None/Small Small Large
Examples Copper Silicon Glass

Key Takeaways

  • Semiconductors are essential for modern electronics.
  • Doping changes conductivity, enabling devices like transistors and solar cells.
  • Ethical concerns include environmental impact and privacy.
  • Ongoing research is making semiconductors thinner, more flexible, and more efficient.

Semiconductor Devices

Figure: Common semiconductor devices (transistor, diode, LED).