Introduction

Semiconductors are materials with electrical conductivity between conductors (like copper) and insulators (like glass). They are foundational to modern electronics, enabling the function of devices such as computers, smartphones, solar cells, and medical equipment. Semiconductors revolutionized technology by allowing precise control of electrical signals.

Main Concepts

1. Atomic Structure and Band Theory

  • Atoms in Semiconductors: Silicon (Si) and germanium (Ge) are the most common elemental semiconductors. They have four valence electrons, forming a crystalline lattice structure.
  • Band Theory: In solids, electrons occupy energy bands. The valence band is filled with electrons, while the conduction band is where electrons can move freely.
    • Band Gap: The energy difference between the valence and conduction bands. Semiconductors have a moderate band gap (e.g., silicon ≈ 1.1 eV).
    • Insulators: Large band gap; electrons cannot easily move.
    • Conductors: Overlapping bands; electrons move freely.

2. Types of Semiconductors

  • Intrinsic Semiconductors: Pure materials (e.g., pure silicon) with equal numbers of electrons and holes.
  • Extrinsic Semiconductors: Doped with impurities to change electrical properties.
    • n-type: Doped with elements (e.g., phosphorus) that add extra electrons.
    • p-type: Doped with elements (e.g., boron) that create “holes” (missing electrons).

3. Charge Carriers

  • Electrons: Negatively charged particles.
  • Holes: Absence of an electron in the valence band, acting as positive charge carriers.
  • Movement: When voltage is applied, electrons and holes move, generating current.

4. Semiconductor Devices

  • Diodes: Allow current to flow in one direction. Used in rectifiers and LED lights.
  • Transistors: Switches and amplifiers. Key to microprocessors and digital circuits.
  • Integrated Circuits (ICs): Complex assemblies of transistors and other components on a single chip.

5. Fabrication Techniques

  • Crystal Growth: Silicon is purified and grown into large single crystals (boules).
  • Wafer Slicing: Boules are sliced into thin wafers.
  • Photolithography: Patterns are transferred onto wafers using light and chemicals.
  • Doping: Introduction of impurities to create n-type or p-type regions.
  • Etching and Deposition: Removing and adding materials to form device structures.

6. Applications

  • Computers and Mobile Devices: Microprocessors, memory chips, sensors.
  • Solar Cells: Convert sunlight into electricity using silicon or newer materials.
  • LEDs and Lasers: Efficient light sources for displays and communications.
  • Medical Devices: Imaging equipment, biosensors.
  • Automotive: Sensors, control systems, electric vehicles.

Recent Breakthroughs

1. Two-Dimensional Semiconductors

  • Research Highlight: A 2021 study published in Nature Electronics details the development of ultra-thin transistors using molybdenum disulfide (MoS₂), a two-dimensional semiconductor. These transistors are only a few atoms thick, offering faster switching speeds and lower power consumption compared to traditional silicon devices (Wang et al., 2021).
  • Significance: Enables further miniaturization of electronics, crucial for advanced computing and flexible devices.

2. Quantum Computing

  • Silicon Qubits: Researchers have created quantum bits (qubits) using silicon, leveraging existing semiconductor manufacturing techniques. This advances the potential for scalable quantum computers.

3. Wide Bandgap Materials

  • Gallium Nitride (GaN) and Silicon Carbide (SiC): These materials operate at higher voltages and temperatures, making them ideal for electric vehicles, renewable energy, and high-frequency communications.

Career Pathways

  • Electrical Engineer: Design and develop semiconductor devices and circuits.
  • Materials Scientist: Research new semiconductor materials and fabrication methods.
  • Process Engineer: Optimize manufacturing processes in semiconductor fabrication plants.
  • Quality Assurance Specialist: Test and ensure reliability of semiconductor products.
  • Semiconductor Physicist: Investigate fundamental properties and behaviors of semiconductor materials.
  • Application Engineer: Work with customers to integrate semiconductor solutions into products.

Future Trends

1. Miniaturization and Moore’s Law

  • Moore’s Law: The number of transistors on a chip doubles approximately every two years. While physical limits are approaching, innovations in materials and design continue to push boundaries.

2. Flexible and Wearable Electronics

  • Organic Semiconductors: Enable bendable, lightweight electronics for medical, sports, and consumer applications.

3. Artificial Intelligence (AI) Hardware

  • Specialized Chips: Semiconductors designed for AI tasks, such as neural processing units (NPUs), are becoming more prevalent.

4. Sustainable Manufacturing

  • Green Processes: Research focuses on reducing energy and water usage in chip fabrication, and recycling semiconductor materials.

5. Integration with Photonics

  • Optoelectronics: Combining electronics with photonics (light-based technology) for faster data transmission and processing.

Conclusion

Semiconductors are vital to modern technology, underpinning devices and systems that shape everyday life. Their unique properties allow precise control of electrical signals, enabling innovations from computers to solar cells. Recent breakthroughs in two-dimensional materials, quantum computing, and wide bandgap semiconductors are driving new possibilities in performance and efficiency. Careers in this field span engineering, research, manufacturing, and applications, offering opportunities to contribute to cutting-edge advancements. As technology evolves, semiconductors will remain central to future trends in electronics, sustainability, and intelligent systems.

Citation

  • Wang, S., et al. (2021). “Ultrathin transistors based on two-dimensional semiconductors.” Nature Electronics, 4, 454–460. Link