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Walter Schottky (; 23 July 1886 – 4 March 1976) was a German physicist, electrical engineer, and inventor who played a major early role in developing the theory of thermionic emission, invented the screen-grid vacuum tube in 1915, co-invented the ribbon microphone and ribbon loudspeaker along with Dr. Erwin Gerlach in 1924, and later made many significant contributions in the areas of semiconductor devices, technical physics, and technology.
The Schottky effect (a thermionic emission; important for vacuum tube technology), the Schottky diode (where the depletion layer occurring in it is called the Schottky barrier), the Schottky vacancies (or Schottky defects), the Schottky anomaly (a peak value of the heat capacity), and the Mott–Schottky equation (also Langmuir–Schottky space charge law) are named after him. He conducted research on electrical noise mechanisms (shot noise), space charge, especially in electron tubes, and the barrier layer in , which were important for the development of metal rectifier and .
Schottky graduated from Steglitz-Gymnasium in Berlin in 1904. He studied under Max Planck and Heinrich Rubens at the University of Berlin, where he received his Ph.D. in 1912 with a thesis titled Zur relativtheoretischen Energetik und Dynamik (On relative theoretical energetics and dynamics).
From 1912 to 1914, Schottky was a postdoc at the University of Jena. In 1916, he joined Siemens & Halske. He then lectured at the University of Würzburg from 1919 to 1922, obtaining his habilitation in 1920. He was a professor of theoretical physics at the University of Rostock from 1923 to 1927, when he returned to Siemens & Halske as an industrial researcher.
In 1944, Schottky's research group moved from Berlin to Pretzfeld. This was also the trigger for the establishment of a semiconductor laboratory of the Siemens-Schuckert-Werke in the castle of Pretzfeld in 1946 until 1955, then he worked in Erlangen until 1958. He lived in Pretzfeld until his death in 1976, where he was also buried.
In 1924, Schottky co-invented the ribbon microphone along with Erwin Gerlach. The idea was that a very fine ribbon suspended in a magnetic field could generate electric signals. This led to the invention of the ribbon loudspeaker by using it in the reverse order, but it was not practical until high flux became available in the late 1930s.
This computes the interaction energy between a point electric charge q and a flat metal surface, when the charge is at a distance x from the surface. Owing to the method of its derivation, this interaction is called the "image potential energy" (image PE). Schottky based his work on earlier work by Lord Kelvin relating to the image PE for a sphere. Schottky's image PE has become a standard component in simple models of the barrier to motion, M( x), experienced by an electron on approaching a metal surface or a metal–semiconductor interface from the inside. (This M( x) is the quantity that appears when the one-dimensional, one-particle, Schrödinger equation is written in the form
The image PE is usually combined with terms relating to an applied electric field F and to the height h (in the absence of any field) of the barrier. This leads to the following expression for the dependence of the barrier energy on distance x, measured from the "electrical surface" of the metal, into the vacuum or into the semiconductor:
This Schottky–Nordheim barrier (SN barrier) has played an important role in the theories of thermionic emission and of field electron emission. Applying the field causes lowering of the barrier, and thus enhances the emission current in thermionic emission. This is called the "Schottky effect", and the resulting emission regime is called "Schottky emission".
In 1923, Schottky suggested (incorrectly) that the experimental phenomenon then called autoelectronic emission and now called field electron emission resulted when the barrier was pulled down to zero. In fact, the effect is due to wave-mechanical tunneling, as shown by Fowler and Nordheim in 1928. But the SN barrier has now become the standard model for the tunneling barrier.
Later, in the context of semiconductor devices, it was suggested that a similar barrier should exist at the junction of a metal and a semiconductor. Such barriers are now widely known as , and considerations apply to the transfer of electrons across them that are analogous to the older considerations of how electrons are emitted from a metal into vacuum. (Basically, several emission regimes exist, for different combinations of field and temperature. The different regimes are governed by different approximate formulae.)
When the whole behaviour of such interfaces is examined, it is found that they can act (asymmetrically) as a special form of electronic diode, now called a Schottky diode. In this context, the metal–semiconductor junction is known as a "Schottky contact".
Schottky's contributions in surface science/emission electronics and in semiconductor-device theory now form a significant and pervasive part of the background to these subjects. It could possibly be argued that – perhaps because they are in the area of technical physics – they are not as generally well recognized as they ought to be.
The Walter Schottky Institute for semiconductor research and the Walter Schottky Prize for outstanding achievements in solid-state physics are named after him. The Walter Schottky House of the RWTH Aachen University and the Walter Schottky Building of the of Applied Sciences in Nuremberg are also named after him. The Fraunhofer Institute for Integrated Systems and Device Technology is located on Schottkystraße in Erlangen.
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