Semiconductors are materials that have conductivity between conductors and insulators. They are neither good conductors nor good insulators as their name says “semi”- conductors.
Semiconductor materials are closely packed crystalline structures. Atoms are so closely packed in crystal lattice that semiconductor materials have very few free electrons. But these electrons are able to move under specific conditions.
Type of Carriers in Semiconductor
We know that carriers are the entities that transport charge from one place to another place within the material. Hence give rise to electrical currents. In everyday life the most commonly encountered type of carrier is the electron which is responsible for charge transport in metallic wires. But in case of semiconductors there are two types of carriers. One is of course “Electrons” and second is “Hole”. Both electrons and holes are equally important in semiconductors. I am assuming that you already have an idea about “What electrons are?” and will discuss holes which I added in this context.
What is Hole?
Hole is simply the absence of an electron. Although it is not a physical particle in the same sense as an electron. Hole can pass from atom to atom in a semiconductor material. Also It considered to have positive charge and holes are positive charge carriers.
Semiconductors can be pure elements like silicon or germanium or compounds such as gallium arsenide or cadmium selenide. These materials such as silicon (Si), germanium (Ge), and gallium arsenide (GaAs) have electrical properties somewhere in the middle or between those of a “conductor” and an “insulator”.
Types of Semiconductor
We can categorized semiconductor into two following types:
- Intrinsic Semiconductor
- Extrinsic Semiconductor
Figure : Types of Semiconductor
Intrinsic Semiconductor: Semiconductor in its purest form known as the intrinsic semiconductor. No impurity added in intrinsic semiconductor. As a result it possesses a very low conductivity level having very few number of charge carriers i.e. holes and electrons. Concentration of holes and electrons are equal in intrinsic semiconductor.
Extrinsic semiconductor: The semiconductor in which impurities are added to the intrinsic semiconductor to make it more conductive is known as the extrinsic semiconductor. Depending upon the type of impurity added the extrinsic semiconductor may be classified as n type semiconductor and p type semiconductor.
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