Bipolar Junction Transistor is a two junction, Bi-Polar, 3-Terminal (Emitter, Base and Collector) device. It is the backbone of every electronic circuit. It is the backbone of every electronic circuit. It is made up of Either germanium (atomic No 32) or Silicon (atomic no.14) The term bipolar reflects.The fact that both holes and electrons participate in the injection process into the oppositely polarized material.
Its outer layers have width much greater than the sandwiched layer.
Construction:- BJT is a 3-Layer device make up from 2- types of semi conductor ( P type & N type) In BJT.A thin layer (Base) of a Semi Conductor material ( P-type or N-type) is Sandwiched between other two layers of some semi-conductor material . Doping level and size of sandwiched layer is kept minimum compare to outer layer.
TYPES:- There are two types of BJT are available.
(i) PNP: In this, holes are majority charge carriers and sandwiched layer is of N-type material.
(ii) NPN: In this electron are majority charge carriers and sandwiched layer is of P-TYPE material
Operation: For proper biasing base-Emitter loop is forward biased and Base Collector loop is reversed biased.
Due to forward biased E.B. Junction, depletion width has been reduced, resulting in heavy flow
Of majority carrier from emitter to Base material . Since the sandwiched layer is very thin & has low conductivity a very small no. of flues carriers will take path of high resistance to the base terminal and a large no of majority carriers diffuse across the reverse biased junction into the collector material.
So IE = IB+IC
And
IC = Ic majority + ICO Minority,
Author: Vipin kumar agrawal