A semiconductor is, by definition, a material that conducts or blocks electricity depending on conditions — but the materials themselves come in many different forms.

In this chapter, we’ll examine the different types and structures of semiconductor materials, laying the groundwork for understanding why a particular material is chosen for a particular purpose.

Semiconductor materials fall broadly into two categories:

Elemental semiconductors → Semiconductors composed of a single element Representative examples: silicon (Si), germanium (Ge)

Compound semiconductors → Semiconductors composed of a compound of two or more elements Representative examples: gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), and others

・Have a stable crystal structure, making them easy to process and mass-produce

・Silicon is the dominant material by far

・Low cost, and form the core of most electronic devices

・Serve as the fundamental material for logic devices such as MOSFETs and ICs

Representative examples:

・Silicon (Si) → The most versatile material — inexpensive, stable, and easy to form an oxide layer on

・Germanium (Ge) → Well suited to high-speed operation, though somewhat inferior in thermal stability

・Offer high electron mobility, making them well suited to high-speed communications and high-frequency devices

・Many are direct-gap materials, allowing them to emit and absorb light (used in LEDs, lasers, etc.)

・Some offer excellent heat and voltage tolerance, making them useful as power semiconductors as well

・On the other hand, they present challenges such as higher manufacturing costs and, in some cases, toxicity

Representative examples:

・GaAs (gallium arsenide) → Optical communications, microwave devices, lasers

・GaN (gallium nitride) → 5G, fast charging, EV power supplies

・SiC (silicon carbide) → EVs, industrial equipment, power control

This is an important classification for understanding how a material interacts with light.

Direct-gap semiconductors Electrons can jump directly from the valence band to the conduction band. → Well suited to absorbing and emitting light (LEDs, lasers) Representative examples: GaAs, InP, GaN, and others

Indirect-gap semiconductors Electrons require the assistance of lattice vibrations (phonons) to make the jump. → Light-emission efficiency is low (as in silicon) Representative examples: Si, Ge

Semiconductor materials can also be classified by the width of their band gap — the barrier that electrons must jump.

・Narrow gap (1 eV or less) → Used for infrared detection (e.g., InSb)

・Medium gap (approximately 1 eV) → General-purpose logic applications (Si, Ge)

・Wide gap (3 eV or more) → Suited to high-temperature and high-voltage applications (SiC, GaN, Ga₂O₃)

Generally, the wider the band gap, the greater a material’s voltage and temperature tolerance — but also the more difficult and expensive it is to process.

Selecting a material requires weighing a combination of factors:

・Electron mobility (speed)

・Band gap (energy barrier)

・Thermal conductivity (heat dissipation performance)

・Mechanical strength

・Cost and availability

・Environmental impact

Which of these factors matters most depends on the intended application. For example: silicon for smartphone CPUs, SiC for EV inverters, and GaN for LEDs.

Going forward, performance is increasingly being optimized not through a single material, but through combined materials and layered structures.

・Si × Ge → High-speed communication chips

・Si × GaN → Energy-efficient power conversion

・Organic × inorganic → Flexible displays, medical sensors

Combining materials in new ways is set to drive the next semiconductor revolution.

・Semiconductor materials are broadly divided into elemental semiconductors and compound semiconductors.

・Direct-gap materials are advantageous for optical applications, while compound materials with high electron mobility are advantageous for fast response.

・Balancing performance, cost, and environmental impact according to the application is essential.

・Going forward, hybridizing dissimilar materials and adopting 3D structures will become the mainstream approach.

1.What is the difference between an elemental semiconductor and a compound semiconductor?

2.Which type of semiconductor is used in LEDs?

3.Why does silicon remain the dominant material?

 

Column Supervisor: Koji Kakumoto (Otis Group Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined Otis Group Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as Representative Director, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.