SOLUTION

• A pure silicon crystal or germanium crystal is known as an intrinsic semiconductor.
• For most applications, there are not enough free electrons and holes in an intrinsic semiconductor to produce a usable current.
• The majority of carriers in a semiconductor are produced by doping.
• The electrical action of these can be modified by doping means adding impurity atoms to a crystal to increase either the number of free holes or the number of free electrons.
• When a crystal has been doped, it is called an extrinsic semiconductor.
• They are of two types n-type semiconductors having free electrons as majority carriers, p-type semiconductors having free holes as majority carriers.
• By themselves, these doped materials are of little use.