How Does Doping Change a Semiconductor?

What you will learn

• Distinguish intrinsic from doped material.
• Compare how n-type and p-type doping create carriers.
• Explain a hole as a missing electron.

Before you start

Read the linked prerequisite first. This article explains principles and does not require assembling or opening equipment.

Deliberately changing a lattice

An intrinsic semiconductor is pure material that has not been doped. Introducing selected impurity atoms into its lattice to modify electrical properties produces an extrinsic semiconductor.

The word “impurity” can misleadingly suggest any contamination is useful. Doping is an intentional choice of introduced atoms, rather than a substitute name for arbitrary dirt.

• Left — n-type dopant site
• Right — p-type dopant site
• Ring marking a missing electron

How do n-type and p-type doping differ?

In n-type doping, the introduced element has more valence electrons than the host, increasing free charge carriers. In p-type doping, it has fewer valence electrons, leaving a missing-electron site called a hole.

Both can increase conductivity in this description. Thus n should not mean “conducting” and p “nonconducting”. The difference is how carriers arise.

A hole is not a drilled opening

A hole describes a missing electron in the electronic arrangement, not a visible cavity between pieces of material. Separate drawings of atomic sites and missing electrons help avoid this confusion.

When reading a doping diagram, identify the host, the introduced atom site and the change in electrons. That explains the electrical change rather than merely naming n-type and p-type material.

A worked example

Start with a pure lattice (an intrinsic semiconductor) and follow two doping routes. This is a conceptual model, not a doping ratio or manufacturing recipe. Route one: replace one site of the host material with an atom that has more valence electrons. The extra electron becomes a free charge carrier, so the material conducts better than before; this is n-type. Route two: replace one site with an atom that has fewer valence electrons. The place where an electron is missing is called a hole; this is p-type.

Look at the outcome of both routes: either material can conduct better, but the carriers arise in two different ways. After doping the material is called extrinsic. One more question to try: why is a speck of dust landing on the material not doping?

Frequently asked questions

Is doping only n-type?

No. P-type doping creates holes as described above.

Can package colour identify the doping type?

This article concerns material properties and provides no package-colour identification rule.

Summary

• Doping changes electrical properties with selected atoms.
• N-type and p-type doping create carriers differently.
• A hole is a missing electron in the electronic picture.