Semiconductors and Communication System

This chapter can be divided into following categories:-

• Classification
• Types of Semi-Conductors
• p-n junction diode
• Biasing of Diode
• Rectifiers
• Special Diodes (Zener, Photodiode, LED and Solar Cell)
• Transistors
• Logic Gates
• Communication System

In the next few posts I will be posting in the same manner ie. (in bullets form) for your convenience and I hope that helps you in completing your syllabus.

Classification

• Materials can be classified on the basis of conductivity as Conductors, Insulators and Semi Conductors.
• The basic difference among all the three is the difference of energy in between the Conducting and the Valence band. This can be seen here.

Note- The range of conductivity should be kept in mind.

• For Semi-Conductors the energy difference is not very large but not even very less. So by providing proper conditions they can show conductivity.

Types of Semi-Conductors

• Further we can say that there are two other types of semi conductors. One of them is naturally occurring (Intrinsic).

• As we can see here when we provide a bit of energy to the intrinsic semi conductors then the electrons jumps in the conducting band. 
• This results in the formation of holes which can be considered as positive charge and when potential difference is applied the holes move in the opposite direction of electrons.
• Also no. of holes = no. of conducting electrons
• Hence we can conclude that by increasing the temperature of Intrinsic Semi conductors the resistance decreases and the current increases.
• The other type is doped semi conductor (Extrinsic). It is made by doping either pentavalent (n type) or trivalent (p type) species in tetravalent specie. These diagrams will help you understand the concepts fully.

PN Junction Diode

• The PN junction can be made by doping a single bar of semi conductor with one side as n type and the other as p type.
• Due to this reason a junction form at the middle of the bar and that causes an electric field which act as a barrier for the current the flow. 
• For numerical point of view if the resistance is given then you just have to solve the circuit like you solve a resistance circuit.
• There are two types of biasing. If the electric field formed is reduced due to the presence of a potential difference the that type of biasing is called Forward Biasing. And vice versa for Reverse Biasing.

NOTE-Do keep in mind that the p side is at the lower potential an n side is at higher potential.

• The following diagrams will help you a lot.
• Do remember the value of threshold voltage.
• Also for reverse biasing it is considered as open circuit and the problems are solved in that way only.