We know from electrical theory, that in order to conduct electricity a material must contain mobile charge carriers. The higher the density of mobile charge
carriers within the material, the better the conductor it will be. When considering metal conductors the mobile charge carriers involved are free electrons. With
semiconductors, we need to be able to understand conduction both in terms of free electrons and also in terms of virtual mobile charge carriers, (i.e. positively
We also need understand how the mobile charge carriers produced by doping and those due to "electron hole pair generation", contribute differently to the
characteristics of semiconductor devices.
As is the case with general electrical theory, we will also have to understand the difference between electron flow and conventional current flow. (When we describe currents flowing in circuits containing semiconductor devices, conventional current flow is commonly used.)