Basics of Digital Electronics Part 1

Semiconductors

               Semiconductors are those materials whose conductivity lies between insulators and conductors.
( Conductors- which allow current to pass through them, Insulators-Does not  allow current to pass)

              These are of two types Intrinsic and Extrinsic Semiconductors. Intrinsic semiconductors are pure semiconductors. When impurity is added to pure semiconductors to increase their conductivity then Extrinsic semiconductors are formed and the process of adding impurity is known as doping.

              When a pentavalent impurity is added then conductivity increases due to free electrons and the semiconductors formed is known as N-Type semiconductor. If a trivalent impurity is added then increased conductivity is due to holes and the semiconductor is known as P-Type semiconductor.

                                

              When P-type and N-type semiconductors are combined then electrons form N-type moves towards P-Type and makes covalent bond in P-Type near the junction and holes from P-type moves towards N-Type . Due to this a potential barrier is created near the junction which is 0.7 v in Si and 0.3 v in Ge.                 

               

                  when PNP or NPN materials are combined then Bi Junction Transistors(BJT's) are formed. 

          Transistors can be used as an amplifier or as a switch.

                  Both PNP and NPN Transistors can be used as solid state switches by biasing the transistor bases. When base of the transistor is triggered then it acts like a closed switch and in the absence of triggering it acts like an open switch.

                                     
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