Explain the construction of a NPN transistor?

Answer 1

An NPN transistor is formed by introducing a thin region of P-type semiconductor material between two regions of N-type material.The layers of an NPN transistor must have the proper voltage connected across them. The voltage of the base must be more positive than that of the emitter and the voltage of the collector must be more positive than that of the base.
The emitter supplies electrons. These electrons are pulled to the base from the emitter because it has a more positive voltage than the emitter. This movement of electrons creates a flow of electricity through the transistor.

PS: P- type is formed by adding acceptor impurities like Boron to Silicon structure.Here holes are majority carriers and electrons are minority carriers.
N-type is formed by adding donor impurities like Phosphorus.Here electrons=majority and holes=minority carriers

Hope this helps

Answer 2

A typical NPN transistor is a three terminal that really is just two diode devices in one. A diode is primarily made of a positively doped semi-conductor material in junction with negatively doped semiconductor material. An NPN is given its name because the construction of the transistor is negative-positive-negative meaning that body terminal hinges the two diode junctions creating the other two terminals the collector and base. A diode's function is to block current one way while allowing it to pass through from the other direction. Just image a device that limits current into a terminal from both sides while allowing it to pass through the other pins quite freely.