Electronic Components of Semiconductors
Conductors --- like copper and gold --- allow the free flow of electricity. Insulators --- like carbon and glass --- inhibit the flow of electricity. Semiconductors are materials that fall in the mid range between conductors and insulators. When people use the word "semiconductor," however, they usually mean a specific semiconductor that has revolutionized electronics.
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Semiconductors
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The semiconductor that is responsible for physicists Shockly, Bardeen and Brattain's 1956 Nobel Prize is basically a crystal, a repeating three-dimensional grid of silicon or germanium atoms locked in place by the six electron orbits they share with the neighboring atoms. In the pure crystal state it is a semiconductor. Electricity will flow through it, but not easily. This changes in an interesting way when some of the atoms in the lattice are replaced by atoms that are very similar to silicon or germanium --- atoms with one fewer or one more electron than all the other atoms in the semiconductor.
Doped Semiconductors
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Baking the semiconductor in an oven filled with a gas until some of the atoms in the gas replace some of the atoms in the semiconductor is a process called "doping." If the atoms in the gas contain one more electron than the atoms in the crystal, the doped semiconductor is called N-type --- negative type, because there are extra electrons floating around the semiconductor. If the atoms in the gas contain one less electron than the atoms in the crystal, the doped semiconductor is called P-type --- positive type, because there are "holes" --- the absence of electrons --- floating around the semiconductor. Holes and free electrons are the electronic components of semiconductors that carry the electricity through diodes and transistors.
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Diodes
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Diodes consist of two dissimilar chips of semiconductor forced together. When a negative potential is applied to a P-type semiconductor it attracts all the holes. When a positive potential is applied to a P-type semiconductor it repels all the holes. When a negative potential is applied to an N-type semiconductor it repels all the free electrons. When a positive potential is applied to an N-type semiconductor it attracts all the free electrons. When a diode is biased in one direction it pulls the holes and electrons away from the NP junction. Biased the other way it propels holes and electrons toward the NP junction. A diode is a device that allows current to flow in one direction but not in the other direction.
Transistors as Amplifiers
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Transistors are composed of three slices of semiconductor material where the middle slice is different from the two outer slices. Flow across the transistor can be controlled by applying a small potential to the center slice. A small signal applied to the center slice is faithfully reproduced on a grander scale in the current flowing through the transistor.
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