What is Semiconductor?

A semiconductor is a crystal material, whose electrical conductivity is between that of a conductor and that of an insulator. It has ability to conduct electricity rises as its temperature goes up. That is, it sometimes acts as a conductor and sometimes as an insulator. Its conducting ability can be much increased by chemical treatment.
A manufactured chip of silicon, less than half an inch square, may contain millions of microscopic transistors, which can serve control and memory functions when installed in a computer, automobile, cell phone, DVD player, or microwave oven.
Fig. 1: Semiconductor
A Semiconductor can conduct electricity under some conditions but not others, making it a good medium for the control of electrical current. Its conductance varies depending on the current or voltage applied to a control electrode, or on the intensity of irradiation by infrared (IR), visible light, ultraviolet (UV), or X rays.
A semiconductor device can perform the function of a vacuum tube having hundreds of times its volume. A single integrated circuit (IC), such as a microprocessor chip, can do the work of a set of vacuum tubes that would fill a large building and require its own electric generating plant.

Types of Semiconductor

The specific properties of a semiconductor depend on the impurities, added to it.
An N-type semiconductor carries current mainly in the form of negatively-charged electrons, in a manner similar to the conduction of current in a wire.
A P-type semiconductor carries current predominantly as electron deficiencies called holes. A hole has a positive electric charge, equal and opposite to the charge on an electron. In a semiconductor material, the flow of holes occurs in a direction opposite to the flow of electrons.

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