The answer to the above question is that we know that in order to ensure the proper working of the transistor, the doping level of all the 3 regions must be sincerely taken into consideration. Now, the question appears why this is so? The figure below shows the connection of two diodes:īut it is noteworthy here that, we cannot form a transistor by connecting two back to back diodes. Like NPN transistor, a PNP transistor is also a back to back connection of two diodes. The collector region has the largest area among all but is not doped as high as the emitter.

The base region is the thinnest among all and hence least doped. But the size of the emitter region is greater than the base but comparatively smaller than the collector. Here, the p region is heavily doped than the base and collector region. The three regions can be formed by either gaseous diffusion of p-type and n-type impurities on a semiconductor wafer or by an epitaxial method, in which an intrinsic region is grown on the heavily doped substrate of similar material. The figure below shows the structural arrangement of the PNP transistor having 3 regions: The semiconductor material can be silicon or germanium. Construction of PNP TransistorĪs we have already discussed that a PNP transistor is formed when 2 p-type semiconductors are connected with an n-type semiconductor material. Here, the inward arrow from the emitter to base represents the direction of current conduction. The figure below shows the symbolic representation of the PNP transistor: It is to be noted here that like NPN transistor here also the emitter region is highly doped than the base and collector region. As a small amount of base current is responsible for controlling a large emitter-collector voltage. PNP transistor is a current controlled device. However, carriers for current conduction and biasing arrangement generates the difference. It is almost similar to another type of BJT i.e., NPN transistor. In PNP transistor, an n-type semiconductor is fixed between 2 p-type semiconductor material in order to generate a PNP transistor.

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