Semiconductor Electronics: Materials, Devices and Simple Circuits

Semiconductor devices are the basic building blocks of all the electronic circuits. The solids are broadly classified as metal conductors, semiconductors and insulators on the basis of relative values of electrical conductivity or resistivity and energy bands. Metal conductors are solids with high conductivity and low resistivity. Insulators are solids with very low conductivity and very high resistivity. Semiconductors are the solids with conductivity and resistivity in between the metals and semiconductors. Metal conductors, semiconductors and insulators are also classified according to energy bands of solids. In conductors, conduction band and valence band partly overlap each other. In semiconductors, the valence band is totally filled and the conduction band is empty while in insulators, the valence band is completely filled and the conduction band is empty and the energy gap is quite large. A semiconductor is further classified as intrinsic and extrinsic semiconductor. A pure semiconductor, which is free from impurity, is called an intrinsic semiconductor. A semiconductor in its natural state is less efficient and therefore a small amount of desired impurity is added to it in order to improve its efficiency. This process is called doping and the new semiconductor formed is called extrinsic semiconductor. On the basis of type of impurity added, extrinsic semiconductors are further categorized as p-type and n-type semiconductors. When a p-type semiconductor is brought in contact with n-type semiconductor crystal, the resulting arrangement is known as a p-n junction or a junction diode. A junction diode called semiconductor diode can work in both forward and reverse biased condition and is used as a rectifier. A junction diode which converts alternating voltages in DC Voltages is called rectifier. A rectifier, which rectifies only one half of each a.c. supply, is called a half wave rectifier. A rectifier, which rectifies both half of the a.c. supply, is called a full wave rectifier. A special type of diode called zener diode is used as a voltage regulator. A zener diode is designed to operate under reverse bias in the breakdown region. Semiconductors are also used as junction transistors. A junction transistor is obtained by growing a thin layer of one type of semiconductor in between two thick layers of other type of semiconductor and thus, a junction transistor can be obtained in two arrangements i.e., p-n-p junction transistor and n-p-n junction transistor. A transistor has its application in various devices like switch, amplifier and an oscillator. In digital electronics, the semiconductor devices use digital circuits for their working. A logical circuit which works according to some logical relationship between input and output voltage is called a logic gate. A logic gate may have one or more inputs but it has only one output. A combination of logic gates are used to form integrated circuits. An integrated circuit is a miniaturized electronic circuit manufactured in the surface of a thin substrate of semiconductor material.

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