A Technological Revolution: The Transistor
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A Technological Revolution: The Transistor
The most significant and revolutionizing discovery of the twentieth century was the electrical characteristics of semiconductors. The idea of semiconductors can be fully grasped when the band theory of solids is understood. This theory clearly states that for electrical conduction, elements have an orbital line-up of electrons. The lower orbitals are filled first, then the higher ones. If an element has a filled valence orbital, the highest filled conduction band, then it wont conduct electricity well. If the valence and conduction band are the same, then it will conduct electricity. Semiconductors are the ones who have a partially filled valence orbital/band. This allows electrons from a current to hop on the atoms electrons, to create the electrical flow through the band. The band gap, or distance from the valence band to the next conduction band is positively correlated with the electrons disability to conduct electricity. The higher the band gap, the lower the conduction. This is because; when the gap is large the electrons cannot populate the conduction band. With semiconductors, their gap is just enough to conduct electricity, but with the addition of impurities this can be controlled. If an impurity, with higher valence electrons per atom, than that of each atom in the solid being charged is added, it creates a negative charge: after all there are extra electrons. If the impurity with less valence electrons per atom, than that of each atom in the solid, is added, it creates positive “holes” or spaces for electrons to hop. The negative impurity is called an n-type semiconductor and the positive, a p-type. The process of adding impurities is called doping, and it is because of this, semiconductors characteristic can be dictated. It is also interesting to note that with temperature increase, the conductivity of semiconductor increases, because the number of high-in-energy electrons increases, populating the band. It is with the practice of controlling semiconductors that transistors were discovered.
John Bardeen, William Shockley, and Walter Brattain, scientists at the Bell Telephone Laboratories in Murray Hill, New Jersey, were researching the behavior of crystal solids, in specific germanium, as semiconductors. Their goal was to use a semiconductor to create a device that would hold a current and be small enough to replace the traditional vacuum tubes. These tubes were also used for currents, though were too large, energy consuming and overheating. Vacuum tubes were used to amplify sounds in telecommunications, but werent practical. Their last attempt was the use of a purer substance, and as a success, they received the Nobel Prize for