In the first blog, we explored why power semiconductors matter, how they’re set to transform our lives, and why they’re critical for achieving net zero.
In this second post, we’re taking a step back to answer a more fundamental question: What exactly is a semiconductor, and how do we make them work for us?
Semiconductors – what are they?
A semiconductor is a material that can behave either as a conductor or an insulator, depending on how it’s made and how we use it.
- Conductors, such as copper, allow electric current (i.e. electrons) to flow easily.
- Insulators, such as rubber, block the flow of electricity—electrons can’t move freely through it.
And here’s the clever part: we can tune how well a semiconductor conducts electricity using chemistry.
Silicon: The Workhorse of Modern Electronics
The most widely used semiconductor material is silicon, around 80% of all semiconductor devices (or chips) are made from it. That includes the memory and processing chips in the computer or phone you’re using to read this blog.
But silicon isn’t the only option. Other semiconductor materials include:
- Compound semiconductors, made from two or more elements (e.g. silicon carbide (silicon + carbon, SiC) or indium gallium arsenide (indium + gallium + arsenic, InGaAs).
- 2D materials like graphene (carbon) can also have semiconductor properties.
- Organic semiconductors, used in technologies like OLED TVs (OLED = Organic Light-Emitting Diodes).
Figure 1: The unit cell of silicon, the balls are silicon atoms and the sticks are the bonds that hold them together and a purified silicon crystal. The unit cell is repeated over and over again in 3D to form the crystal. Image source: https://en.wikipedia.org/wiki/Silicon
Doping: Turning Insulators into Semiconductors
Pure silicon is actually an insulator. Each silicon atom has four electrons available for bonding, and it forms strong bonds with four neighbouring atoms, creating a stable crystal structure. These electrons are tightly bound and can’t move—so no electricity flows.
To make silicon useful for electronics, we need to change how it behaves. This is where doping comes to the fore, which is achieved by adding tiny amounts of other elements to the silicon. There are two main types of doping:
N-type Doping
N-type doping is where we replace a silicon atom with an elements like phosphorus or arsenic (from Group 5 of the periodic table), which have five electrons available for bonding. When one of these atoms replaces a silicon atom, four electrons form bonds with neighbouring silicon atoms, but the fifth electron is left over and is free to move.
This extra, mobile electron gives us a negatively charged carrier, hence n-type doping.
P-type Doping
P-type doping is when we substitute elements like boron or gallium (from Group 3), which have only three outer electrons. When one of these atoms is introduced into the silicon structure, one of the usual four bonds ends up missing an electron, leaving a “hole” where an electron could go. Electrons from nearby atoms can move into this hole, effectively causing the hole itself to “move” through the structure.
These are positive charge carriers, so we call it p-type doping.
To change the properties of the semiconductor we only need to replace a tiny number of silicon atoms, as little as one in every billion!
Figure 2: doping silicon to create free charge carriers
Why Is This Useful?
So now we’ve turned silicon from an insulator into something that can carry current. But metals like copper conduct electricity better, so what makes semiconductors special?
The magic happens when you put n-type and p-type materials together. This boundary, called a p-n junction, is the foundation of diodes, transistors, solar cells, and virtually every modern electronic device.
We’ll explore what happens at this junction in the next post in the “Power Semiconductors for Everyone” series!