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.