Semiconductor devices and circuits - Coursework Example

Each atom after sharing electrons will attain a full outer shell. Conductors: Conductor materials have large number of free electrons and thus conduct easily. Examples of a good conductor are copper and aluminum and they have, at room temperature, many electrons for conduction. Insulators These are materials which do not conduct. For insulators, there is a very large gap between the two bands i.e. conduction and valence bands. Insulators can only conduct at extremely high temperatures or when they are subjected to very high voltage.

Examples of insulators are, wood, glass, paper and mica. Semiconductors: These materials are between conductors and insulators. They are neither conductors nor insulators. They can easily conduct at room temperatures. Examples of these materials are silicon and germanium. Intrinsic semiconductors: These are pure semiconductors since the content of impurity is minimal. These materials are cautiously refined to achieve this form of purity. When intrinsic semiconductors are subjected to room temperature, valence electrons absorb heat energy breaking the covalent bond and move to conduction band.

Electrons and holes conduction In intrinsic semiconductors, holes and free electrons are the major charge carriers. Holes and electrons which are generated at room temperatures move in a random motion and can’t conduct any current. . This allows electric current to flow as a result of electrons movement in the conduction band. The motion of holes in semiconductors is opposite to that of electron. As a result of electrons escape from valence band to conduction band, holes are created in the valence band.

When current is applied the electron break and moves to feel the holes present, at the same time this electron leaves another hole and this process continues. The movement of these holes in the valence band leads to current flow referred to as whole current. Extrinsic Semiconductors Small amounts of other materials are added to intrinsic semiconductor to alter the properties and this result to extrinsic semiconductor. This is process of adding an impurity to improve the conductivity of the semiconductor is referred to as doping.

The materials used as impurities are called dopant. These semiconductors are the most widely used in practice since they have better conductivity compared to intrinsic semiconductors and are used in manufacture of electronics components such as transistors and diodes. There are two types of extrinsic semiconductors and each depending on the type of impurity used. They are n-type and p-type. N- Type Atoms with five electrons in their outer most shell are referred to as pentavalent atoms. When these pentavalent atoms are used to dope intrinsic semiconductors, they donate a free electron to the semiconductor and they are called donor dopers.

Examples of donor materials are phosphorous, arsenic and bismuth. The resulting semiconductor has a large quantity of free electrons and is called n-type semiconductor. Example of n-type semiconductor formation is when arsenic atom with five electrons on the outermost shell combines with silicon with four