Compare the Bipolar Junction transistor and Field effect transistor.
Answers
Difference Between BJT and FET
What is BJT?
The BJT is a one type of transistor that uses both majority and minority charge carriers. These semiconductor devices are available in two types such as PNP and NPN. The main function of this transistor is to amplify current. These transistors can be used as switches and amplifiers. The applications of BJTs involve in a wide range that includes electronic devices like TVs, mobiles, computers, radio transmitters, audio amplifiers and industrial control.
Bipolar Junction Transistor
Bipolar Junction Transistor
Construction of BJT
A bipolar junction transistor comprises of two p-n junctions. Depending on the structure of the BJT, these are classified into two types such as PNP and NPN. In NPN transistor, lightly doped P-type semiconductor is placed between two heavily-doped N-type semiconductors. Equally, a PNP transistor is formed by placing an N-type semiconductor between P-type semiconductors. The construction of a BJT is shown below. The emitter and collector terminals in the below structure are called n-type and p-type semiconductors which are denoted with ‘E’ and ‘C’. While the remaining collector terminal is called p-type semiconductor denoted with ‘B’.
Construction of BJT
Construction of BJT
When a high voltage is connected in reverse bias mode across both the base and collector terminals. This roots a high depletion region to form across the BE junction, with a strong electric field that stops the holes from the B-terminal to the C-terminal. Whenever the E and the B terminals are connected in forward bias, the flow of electrons direction will be from the emitter terminal to the base terminal. In the base terminal, some electrons recombine with the holes, but the electric field across the B-C junction attracts electrons. Most electrons end up overflowing into the collector terminal to create a huge current.
Since the flow of heavy current through the collector terminal can be controlled by the small current through the emitter terminal. If the potential difference across the BE junction is not strong, then the electrons are not able to get into the collector terminal so, there is no flow of current through the collector terminal. Due to this reason, a bipolar junction transistor is used as a switch as well. The PNP junction also works with a same principle, but the base terminal is made with a N-type material and the majority charge carriers in the PNP transistor are holes.