Jun 19, 2023

What Is a Semiconductor?

A semiconductor is a material that controls electrical currents, making it an essential component of most modern electronics. They are the computing chips and microcontrollers that power smartphones, computers and televisions.

The unique properties of semiconductors position them in between high-conducting materials (like copper or aluminum) and nonconductors (like rubber or glass). Most commonly made out of silicon, germanium and gallium arsenide, semiconducting hardware either allows a free flowing current or repels it completely.

Semiconductors are materials that can control the flow of electricity more than insulators (nonconductors) but less than conductors. They are used in many electronic devices, including computers and smartphones.

“Every electronic device that plugs into a wall or uses a battery has semiconductors in it,” Mike Pienovi, general manager of Sitara microcontroller units at Texas Instruments, told Built In.

It’s hard to overstate the ubiquity of semiconductors: Diodes, chips and transistors are all devices made out of them.

“Semiconductors are in a wide range of markets such as industrial, automotive, personal electronics, communications equipment and enterprise systems,” Pienovi added. “These chips are a crucial component of today’s technology, affecting nearly every aspect of our lives.”

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A semiconductor’s ability to conduct electricity depends on the movement and interaction between its two current carriers: free electrons and holes (which represent the absence of an electron).

“To understand how semiconductors work,” according to PhD-qualified chemist Andrew Stapleton, who creates content at Academia Insider, “you need to know about energy bands.”

Stapleton explained it like this: In solids, electrons occupy energy levels that form energy bands. The two most relevant energy bands in semiconductors are the valence band (which is filled with valence electrons) and the conduction band (which is largely vacant).

As thermal energy is applied to semiconducting material, valence electrons move from the valence band to the conduction band, where they become free electrons. They leave behind empty spots in the valence band, which creates holes.

“In nonconductors, these bands are far apart from one another,” Stapleton said. “But in semiconductors, they're close enough so that, when a heat source is applied, electrons can jump from the valence band to the conduction band, enabling the flow of electric current.”

Determining the strength of that current is up to the amount of voltage applied, as well as the properties of a semiconducting material (more on that below). The relationship between these factors is described by Ohm's Law, which establishes that an electrical current is directly proportional to the applied voltage yet inversely proportional to a material’s resistance.

Resistance, however, can be manipulated in order to better control the flow of electric currents. In a process known as doping, the number of current carriers can be increased by adding impurities to a material. By upping the number of free electrons or holes, a majority is created among current carriers, which results in stronger conductivity.

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Intrinsic semiconductors are pure materials, namely silicon and germanium, that have a natural ability to conduct electricity when in contact with a heating element. As is, however, these undoped materials do not conduct electrical currents very well.

In intrinsic semiconductors, the number of free electrons in the conduction band will always be equal to the number of holes in the valence band. This low-concentration of current carriers — free electrons and holes — results in poor conductivity at room temperature. Improving their conductance is heavily reliant on an external thermal energy source, such as voltage.

So while the ability to conduct electricity alone makes semiconductors a useful component, this ability is limited in intrinsic, or I-type, semiconductors.

“Extrinsic semiconductors,” Vikas Kaushik, CEO of mobile app development company TechAhead and computer science graduate, explained, “are impure materials deliberately ‘doped’ with specific elements to enhance their electrical properties.”

In other words, if you want to enhance conductivity, you need to add more electrons, or more holes — anything to create an unequal number of them. This is where extrinsic materials come in.

To add more electrons, a semiconductor is doped with an atom that contains five valence electrons, known as pentavalent atoms. To increase the number of holes, atoms with three valence electrons, or trivalent atoms, are used.

Semiconductors that carry more electrons are N-type semiconductors, while those with a hole majority are classified as P-type semiconductors.

Extrinsic semiconductors are more commonly used to build electronics than their intrinsic counterparts.

Before semiconductors came along, scientists built the first generation of computers using vacuum tubes. An estimated 17,468 of these glass-encased tubes, resembling miniature light bulbs, were built into the world’s first digital computer, the ENIAC, which was introduced in 1964. While this system took up entire rooms, weighing 30 tons and standing nine feet tall, its capabilities were nowhere near the pocket-sized smartphones of today.

With the advent of transistors in 1947, semiconductors became synonymous with the information age.

“Semiconductors play an indispensable role in technology and innovation,” Kaushik said. “They are the backbone of microprocessors, enabling computers to perform complex tasks with speed and efficiency.”

A single semiconductor chip contains millions of transistors. Today, there are more than 100 billion integrated circuits in daily use around the world, according to the Semiconductor Industry Association. Since coming onto the scene in the mid-century, semiconductors have been featured at the core of nearly every electronic device of the past, and continue to power future tech, including artificial intelligence, autonomous cars and Internet of Things devices.

“Innovation is continuing to make semiconductor technology smaller, more efficient, more reliable and more affordable,” Texas Instruments' Pienovi said.

As Kaushik sees it, semiconductors underpin the very foundation of modern electronics and digital transformation. “Without semiconductors,” he said, “the digital landscape as we know it would not exist.”

When it comes to the next generation of semiconductors, though, the challenge lies in cutting carbon emissions by 50 percent over the next decade, toward a net-zero production.

A semiconductor is a material that can control and manage the flow of electrical currents. Their unique properties of conductivity position them between conductors and nonconductors.

Semiconductors are used to build virtually every electronic device and have applications across most relevant sectors, such as automotive, home electronics, communications equipment and enterprise systems.