We looked at pure or intrinsic semiconductors in the previous post on Analog Electronics. We can however, change the electrical properties of the pure semiconductors by adding certain impurities to their structure, a process called doping. In this post, we talk about semiconductor devices where we will cover the doping process and also extrinsic semiconductors.
When doping semiconductors of groups 3 & 4, these impurities are usually elements of group 3 (acceptors) or 5(donors).
This gives rise to two kinds of extrinsic semiconductors : ones having free electrons as their majority charge carriers(called n-type) & those which have holes as their majority charge carriers(called p-type).
Extrinsic semiconductors are used in many electrical devices. A more useful version of doped semiconductors is the p-n junction.