1.01 Semiconductor Theory

The term semiconductor refers to the electrical properties of certain materials. Materials are classified as conductors, semiconductors or insulators depending on how well they conduct electricity. Conductors as the name implies are materials that electrical current can flow through very easily, while insulators strongly resist current flow.

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

Mobile Charge Carriers

It is the abundance (or lack of) mobile charge carriers within a material that determines its natural conduction properties. Conductors contain a very high density of mobile charge carriers (in the order of 1028 per m3), insulators have very few.
In conductors the mobile charge carriers are free electrons (i.e. electrons which are not bound to their parent atoms and can move freely within the material).

Intrinsic and Extrinsic Semiconductor

In this section we will examine the natural (or intrinsic) conduction properties of the semiconductor materials that are used to make electronic components. First we will consider the atomic structure of pure silicon to understand why it has no mobile charge carriers at a temperature of 0K. We will then consider how thermal energy can produce two types of mobile charge carriers in a process called electron - hole pair generation. We will then go on to look at how pure silicon is modified to produce two different types of extrinsic semiconductor materials called P and N type semiconductor that have significantly enhanced conduction properties. Finally we will consider the structure and operation of some fundamental electronic components that are made using P and N type semiconductor starting with the most basic component, the semiconductor diode.