Hall Effect

Of monumental importance to today's technology is a class of materials whose ability to conduct electric current increases with temperature and whose charge carriers can be either positive or negative, depending on the impurity introduced into them. These materials are called semiconductors, prime examples of which are the elements silicon and germanium. When these elements are given traces of the appropriate impurity element, they can be made into either p-type (containing positive carriers called holes) or n-type (containing negative carriers called electrons). The Hall effect is then used to confirm which type of material one is dealing with. Furthermore, by measuring the Hall potential, the current, the magnetic field, and the sample geometry, it is easy to calculate the number of charge carriers per unit volume in the material tested. In the 1940s, it was found that junctions could be formed with these two different types of semiconductors across which current could flow only in one direction. Devices of this kind are called rectifiers or diodes and are vital for converting alternating current to direct current, adding or removing audio and video signals from their carrier waves, and many other applications. It was also found that more than two junctions could be formed in one device, and these were called transistors. These devices were capable of being employed in amplifier and oscillator circuits in radios and TVs. Previously, rectifiers, amplifiers, and oscillators used vacuum tubes as their essential components, which were generally bulky, used lots of power, and burned out frequently. The new semiconductor devices had none of these problems. In the 1950s and 1960s, it was learned how to create many transistor circuits on a small chip using integrated circuitry. Without this new technology, the powerful computers that were used in our space program and are now found universally in the form of compact personal computers would not have been possible. Even more importantly, without the discovery of the Hall effect and its use in the scientific investigation of semiconducting materials, this sequence of developments could not have even begun. Finally, with the discovery of its large-scale quantum behavior, the future role of the Hall effect in the advancement of science and technology may eventually prove to be even greater than its past role.