Electricity is the flow of electrons.

When electrons move, “current” is generated.

Batteries and generators supply the force that pushes electrons into motion — this force is called voltage.

How freely electrons can move differs depending on the material.

・Conductor: Electrons can move freely. Examples: copper, silver, aluminum

・Insulator: Electrons can barely move at all. Examples: glass, rubber, paper

・Semiconductor: How electrons move changes depending on conditions. Examples: silicon, germanium

Within a material, electrons occupy “energy levels” known as bands. Whether or not electricity flows depends on which band the electrons occupy.

・Valence Band: The region where electrons normally reside

・Conduction Band: The region where electrons can move freely

Between the valence band and the conduction band lies a barrier called the “band gap.” The smaller this barrier, the more easily electrons can move.

・Conductor: The valence band and conduction band overlap → electrons can move freely

・Semiconductor: A small band gap exists → electrons can cross it under certain conditions

・Insulator: A large band gap → electrons cannot move

In short, a semiconductor is a material with a barrier height that electrons can “jump” depending on temperature or light.

The flow of electricity involves not only electrons (negative) but also “holes” (positive vacancies).

When an electron moves to the right, a vacancy is left behind on the left.

This vacancy, treated as though it were a positive particle, is called a “hole.”

・Flow of electrons → the negative direction of current

・Flow of holes → the positive direction of current

Together, these two movements form the current within a semiconductor.

In metals (conductors), as temperature rises, electron movement is increasingly disrupted, making it harder for electricity to flow.

In semiconductors, by contrast, rising temperature excites electrons, making them move more easily and allowing electricity to flow more readily.

In other words, the relationship between temperature and electrical behavior is reversed between conductors and semiconductors.

When light strikes a semiconductor, electrons absorb the light energy and jump from the valence band to the conduction band.

The resulting flow of current is known as the “photoconductive effect.”

This property is applied in image sensors used in cameras, optical sensors, and similar devices.

Applying voltage accelerates the movement of electrons and holes, generating current.

A device designed to allow current to flow in only one direction is called a “diode.”

This ability to control current flow is precisely what gives semiconductors their greatest value.

・Electricity is the flow of electrons.

・Conductors, semiconductors, and insulators are classified based on how freely their electrons can move.

・In semiconductors, the movement of electrons changes in response to temperature, light, and voltage.

・These properties are harnessed to create switches, sensors, and transistors.

1.What does it mean for electricity to flow?

2.What are the main factors that cause a semiconductor’s conductivity to change?

3.What is a correct way to describe the difference between a semiconductor and a conductor?

 

 

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.