Electric contact in transistors and related devices between two different types of material called p-type and n-type semiconductors. These materials are pure semiconductor materials, such as silicon, to which impurities have been added. Materials of p-type contain holes (vacancies formerly occupied by electrons) that behave like positively charged particles, whereas n-type materials contain free electrons. Electric current flows more easily across a p-n junction in one direction than in the other. If the positive pole of a battery is connected to the p-side of the junction, and the negative pole to the n-side, charge flows across the junction. If the battery is connected in the opposite direction, very little charge can flow. The p-n junction forms the basis for computer chips, solar cells, and other electronic devices.
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