Semiconductor Electronics: Materials, Devices and Simple Circuits

•    All the electronic devices make use of semiconductor materials.
•    All solids can be broadly classified as metal conductors, semiconductors and insulators on the basis of relative values of electrical conductivity or resistivity and energy bands.
•    Solids with high conductivity and low resistivity are known as conductors.
•    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.
•    On the basis of energy band diagram solids are classified as conductors, semiconductors and insulators.
•    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.
•    In semiconductors the gap between valence band and conduction band is moderate.
•    In insulators, the valence band is completely filled and the conduction band is empty and the energy gap is quite large.
•    On the basis of impurity atoms a semiconductor is further classified as intrinsic and extrinsic semiconductor.
•    A pure semiconductor, which is free from all impurities, is known as an intrinsic semiconductor.
•    A small amount of impurity is added to pure intrinsic semiconductor to make it conduct at all temperatures.
•    This process of adding impurity is called doping and the new semiconductor formed is called extrinsic semiconductor.

•    Extrinsic semiconductors can be further categorized on the basis of type of impurity added, 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.
•    In a junction diode a p-type semiconductor is joined to an n-type semiconductor. It can be used as a rectifier.
•    Rectifier is a device which converts AC into DC. 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.
•    Zener diode is a special type of diode used as a voltage regulator. It is designed to operate under reverse bias in the breakdown region.


                                         

•    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.
•    Some of the applications of transistor are switch, amplifier and an oscillator.
•    Semiconductor devices use digital circuits for their working in digital electronics.
•    A logical circuit which works according to some logical relationship between input and output voltage is known as logic gate.
•    A logic gate may have multiple inputs but it has only one output. Integrated circuits are formed by a combination of logic gates.
•    An integrated circuit is a miniaturized electronic circuit manufactured in the surface of a thin substrate of semiconductor material.

 

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