Walter H. Schottky

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Walter H. Schottky bigraphy, stories - German physicist

Walter H. Schottky : biography

23 July 1886 – 4 March 1976

Walter Hermann Schottky (23 July 1886 – 4 March 1976) was a German physicist who played a major early role in developing the theory of electron and ion emission phenomena, invented the screen-grid vacuum tube in 1915 and the pentode in 1919 while working at Siemens, co-invented the ribbon microphone and ribbon loudspeaker along with Dr. Gerwin Erlach in 1924 and later made many significant contributions in the areas of semiconductor devices, technical physics and technology.

Early life

Schottky’s father was mathematician Friedrich Hermann Schottky (1851–1935). Schottky’s father and mother had one daughter and two sons. His father was appointed professor of mathematics at the University of Zurich in 1882, and Schottky was born four years later. The family then moved back to Germany in 1892, where his father took up an appointment at the University of Marburg.

Schottky graduated from the Steglitz Gymnasium in Berlin in 1904. He completed his B.S. degree in physics, at the University of Berlin in 1908, and he completed his Ph.D. in physics at the University of Berlin in 1912, studying under Max Planck and Heinrich Rubens, with a thesis entitled: Zur relativtheoretischen Energetik und Dynamik.

Career

Schottky’s postdoctoral period was spent at University of Jena (1912–14). He then lectured at the University of Würzburg (1919–23). He became a professor of theoretical physics at the University of Rostock (1923–27). For two considerable periods of time, Schottky worked at the Siemens Research laboratories (1914–19 and 1927–58).

Books written by Schottky

  • Thermodynamik, Julius Springer, Berlin, Germany, 1929.
  • Physik der Glühelektroden, Akademische Verlagsgesellschaft, Leipzig, 1928.

Inventions

In 1924, Schottky co-invented the ribbon microphone along with Gerwin Erlach. The idea was that a very fine ribbon suspended in a magnetic field could generate electric signals. This led also to the invention of the ribbon loudspeaker by using it in the reverse order, but it was not practical until high flux permanent magnets became available in the late 1930s.

Controversy

The invention of superheterodyne is usually attributed to Edwin Armstrong. However, Schottky published an article in the Proceedings of the IEEE that may indicate he had invented something similar.

  • 1939: first p–n junction

Major scientific achievements

Possibly, in retrospect, Schottky’s most important scientific achievement was to develop (in 1914) the well-known classical formula, now written −q2/16πε0x, for the interaction energy between a point 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

frac Psi(x) = frac{hbar^2} M(x) Psi(x) .

Here, hbar is Planck’s constant divided by 2π, and m is the electron mass.)

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:

M(x) = ; h -eFx – e^2/4 pi epsilon_0 epsilon_r x ;.

Here, e is the elementary positive charge, ε0 is the electric constant and εr is the relative permittivity of the second medium (=1 for vacuum). In the case of a metal–semiconductor junction, this is called a Schottky barrier; in the case of the metal-vacuum interface, this is sometimes called a Schottky–Nordheim barrier. In many contexts, h has to be taken equal to the local work function φ.