write about the solid state physics of NBN Bipolar Junction Transistor(BJT)

Question

Robert · Accepted Answer

Bipolar Junction Transistor 
Transistor is a 3-layer, two junctions, and three terminal devices. It is made up of either 
Germanium or Silicon. In a transistor, current is carried by both holes and electrons, 
therefore, it is called as bi-polar transistor [Bi-polar reflects the fact that both holes and 
electrons participate in the injection process into the oppositely polarized material. If only 
one type of carriers is employed (i.e. electrons or holes) then it is considered a unipolar 
device. The UJT and schottky diode are such a device]. Bipolar Junction Transistor (BJT) is a 
two junction, bi-polar, 3-terminal device. It is the backbone of every electronic circuit. 
Transistor is the main component in amplifiers, switching circuits, oscillators and logical 
circuits. It is also used to match the impedances of source and load.  
Constructionally, two type of transistors are available; PNP and NPN
(i) PNP: Single N region is sandwiched between two P-regions in a PNP transistor. Holes are 
majority charge carriers in a PNP transistor. A PNP transistor is symbolized as shown above. 
Direction of arrow in symbol indicates the direction of current flow.  
http://s.eeweb.com/members/andrew_carter/blog/2012/01/21/Fundamentals-of-Bipolar-Junction-Transistors-2-1327155249.gif
(ii) NPN: NPN transistor has a P-region sandwiched between two N-regions. In NPN 
transistor the electrons are majority carriers. Mobility of electrons is higher than holes, 
therefore switching speed of NPN transistor is more than PNP transistor and packing density 
of NPN transistor is more than PNP transistor. Direction of arrow indicates that current flow 
from collector to emitter (opposite to direction of flow of electrons).  
Transistor has three layers and these layers are known as Emitter (E), Base (B) and Collector 
(C).  
Emitter: It is most heavily doped. As the name indicates it emits the charges. N-type emitter 
emits electrons and P-type emitter emits holes.  
Base: Base is central portion of transistor. Doping level and size of the base is kept minimum 
among three layers due to following reasons:

write about the solid state physics of NBN Bipolar Junction Transistor(BJT)

Solution

Answer To This Question Is Available To Download

Related Questions & Answers

Submit New Assignment