We discussed about conductors and insulators earlier. There is another group known as semiconductors like germanium and silicon which are bad conductors of electricity in their natural form. If some impurities like boron or antimony are added in minute quantities to these they can have either an increase in free electrons or a deficiency of electrons. Then they become semiconductors. The process of adding impurities is known as doping. When there is a deficit of electrons, it is called a P-type semiconductor. They have positively charged 'holes' as charge carriers. N-type semiconductors on the other hand have excess electrons as charge carriers. Silicon has four electrons in the outermost shell. When it is doped with boron having only three electrons in outer shell, it becomes a P-type semiconductor, with deficit of electrons or 'holes'. Doping with antimony which has five electrons in outer shell makes it an N-type semiconductor, with an excess of electrons. Read More: johnsonfrancis...
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