1.01 Semiconductor Theory

Introduction
There are three basic types of materials that we are concerned with in electronics. These are conductors, semiconductors and insulators.
Materials that have very low electrical resistivity (in the order of 1 x 10-6 ohm-metres) are called conductors.
Materials that have very high electrical resistivity (in the order of 1 x 1013 ohm-metres) are called insulators.
Semiconductors are materials that have resistivity values in between those of conductors and insulators, they are neither good conductors nor good insulators.

Examples of conductors:
  • Copper
  • Aluminium
  • Silver
  • Gold
Examples of insulators:
  • Rubber
  • PVC
  • Paper
  • Mica
Examples of Semiconductors:
  • Silicon
  • Germanium

Semiconductor materials are used to make a range of devices that are used in modern electronic circuits. In order to understand how these devices work we must first gain an understanding of the electrical properties of naturally occurring (intrinsic) semiconductors. We then need to learn about the electrical properties of extrinsic semiconductors. Extrinsic semiconductor material is just a naturally occurring pure semiconductor material that has been modified by a manufacturing process.

First we will look at the atomic structure of intrinsic semiconductors to understand their electrical properties. Then we will look at how this structure is modified to produce extrinsic semiconductor material and how this changes the materials electrical properties. Finally we will look at the construction and operation of a semiconductor diode which is the most basic semiconductor device used in electronic circuits. During this section we will consider "true" electron flow rather than conventional current flow which is used in electrical circuit analysis.