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Basic Semiconductor Physics
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Some substances like Germanium, Silicon, Carbon, etc. are neither good conductors like copper nor insulators like glass. The resistivity of these materials lies in between conductors and insulators. Such substances are known as semiconductors.
Semiconductor devices are very important parts in electronics. There are different types of semiconductor devices like diode, LED (Light Emitting Diode), bi-polar transistor, Integrated Circuit (IC), MOSFET (Metal Oxide Semiconductor Field Effect Transistor), FET, JFET (Junction Field Effect Transistor), SCR (Silicon Controlled Rectifier), etc. They are used in all types of systems for quality control and automation. Semiconductors are very fast in working, have low electrical consumption and long life.
Understanding Semiconductors
The atomic structure and energy gap between valence band and conduction band plays important role in deciding the conductivity of the material. Thus conductivity depends on number of free electrons, to carry electric current.
The pure crystal of semiconductor (Si or Ge) is known as intrinsic semiconductor at room temperature. The Silicon atom has 14 electrons revolving around its nucleus. In first orbit - 2 electrons, in second orbit -8 electrons i.e. 4 electrons in last orbit, known as valence electrons.
The devices like diodes, transistors, ICs used in electronic circuits are manufactured with the help of extrinsic semiconductor. When a trivalent or pentavalent element is mixed with pure Silicon crystal (i.e. intrinsic semiconductor), the new material is formed known as extrinsic semiconductor. The process of adding this element into pure Silicon is called doping. So a doped Si is called extrinsic semiconductor. They are of two types, P-type semiconductor and N-type semiconductor.
Following is the comparison of two types of semiconductors. Learn them and remember the points for understanding the behaviour of semiconductors.
A PN junction diode is the first semiconductor device in semiconductor family. It is also known as unidirectional current device, because it allows current only in one direction through it.
Biasing means connecting a PN junction across the battery or a power supply, in forward or reverse direction.
Complete practical procedure for finding out anode and cathode and whether the diode is ok or not.
In forward biasing of diode, free electrons from N-layer cross the junction and come into P-layer. Then they recombine with holes and then attracted by positive terminal of battery. In reverse biasing, free electrons in N-layer go away from the junction. So they produce more positive ions near the junction.
Applications of PN Junction Diode
Download the complete pdf file of applications of rectifier circuits with formulae, calculations and the related exercise. Also watch the working of rectifier circuits with the help of video lectures.
A diode is a semiconductor device that contains two semiconductor layers known as p-layer and n-layer. It has two terminals ANODE and CATHODE. Inside it there is one junction known as p-n junction. It also acts as potential barrier for the diode. Any diode conducts current only in one direction i.e. from ANODE to CATHODE. Hence it is called unidirectional device.
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Specially designed for the students admitted in 11th standard electronics (C2), computer science (D9) or even general science students. This course is equally useful for B.Sc. and B.E. level students.