History of Transistors;Part-5

During manufacturing of a transistor, the semiconductor material is processed with the addition of small amounts of chemical impurities, such as arsenic or antimony. This process was referred as “doping”. It is required in order to create proper crystalline structure in the semiconductor to allow transistor action. Depending on the doping elements used in semi-conductor material, transistors can be classified as either PNP or NPN. PNP and NPN are representations of the electrical polarity to be used with the transistor. For example, a PNP transistor would require a specific set of Positive and Negative voltage polarities to be used for the three transistor terminals in circuit applications. NPN transistor requires all circuit voltage polarities to be reversed from those used for a PNP. Many circuit applications require the both PNP and NPN transistors..