Walter Schottky
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Walter Hans 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 A tetrode is a vacuum tube (called ''valve'' in British English) having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate (called ''anode'' in British English). Th ...
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
in 1915 while working at
Siemens Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad. The principal divisions of the corporation are ''Industry'', '' ...
, 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 Engineering physics, or engineering science, refers to the study of the combined disciplines of physics, mathematics, chemistry, biology, and engineering, particularly computer, nuclear, electrical, electronic, aerospace, materials or mechanical ...
and technology.


Early life

Schottky's father was
mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History On ...
Friedrich Hermann Schottky Friedrich Hermann Schottky (24 July 1851 – 12 August 1935) was a German mathematician who worked on elliptic, abelian, and theta functions and introduced Schottky groups and Schottky's theorem. He was born in Breslau, Germany (now Wrocław, ...
(1851–1935). Schottky had one sister and one brother. 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 Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitue ...
in 1904. He completed his
B.S. degree A Bachelor of Science (BS, BSc, SB, or ScB; from the Latin ') is a bachelor's degree awarded for programs that generally last three to five years. The first university to admit a student to the degree of Bachelor of Science was the University of ...
in
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
, at the
University of Berlin Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative o ...
in 1908, and he completed his
PhD PHD or PhD may refer to: * Doctor of Philosophy (PhD), an academic qualification Entertainment * '' PhD: Phantasy Degree'', a Korean comic series * ''Piled Higher and Deeper'', a web comic * Ph.D. (band), a 1980s British group ** Ph.D. (Ph.D. albu ...
in physics at the
Humboldt University of Berlin Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative o ...
in 1912, studying under Max Planck and
Heinrich Rubens Heinrich Rubens (30 March 1865, Wiesbaden, Nassau, Germany – 17 July 1922, Berlin, Germany) was a German physicist. He is known for his measurements of the energy of black-body radiation which led Max Planck to the discovery of his radiation l ...
, with a thesis entitled: ''Zur relativtheoretischen Energetik und Dynamik'' (translates as ''About Relative-Theoretical Energetics and Dynamics'').


Career

Schottky's postdoctoral period was spent at
University of Jena The University of Jena, officially the Friedrich Schiller University Jena (german: Friedrich-Schiller-Universität Jena, abbreviated FSU, shortened form ''Uni Jena''), is a public research university located in Jena, Thuringia, Germany. The un ...
(1912–14). He then lectured at the
University of Würzburg The Julius Maximilian University of Würzburg (also referred to as the University of Würzburg, in German ''Julius-Maximilians-Universität Würzburg'') is a public research university in Würzburg, Germany. The University of Würzburg is one of ...
(1919–23). He became a professor of theoretical physics at the
University of Rostock The University of Rostock (german: link=no, Universität Rostock) is a public university located in Rostock, Mecklenburg-Vorpommern, Germany. Founded in 1419, it is the third-oldest university in Germany. It is the oldest university in continen ...
(1923–27). For two considerable periods of time, Schottky worked at the Siemens Research laboratories (1914–19 and 1927–58).


Inventions

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
permanent magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
s became available in the late 1930s.


Major scientific achievements

In 1914, Schottky developed the well-known classical formula, written here as :E_(x) = -\frac . This computes 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 A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
interface from the inside. (This ''M''(''x'') is the quantity that appears when the one-dimensional, one-particle,
Schrödinger equation The Schrödinger equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system. It is a key result in quantum mechanics, and its discovery was a significant landmark in the development of the ...
is written in the form :\frac \Psi(x) = \frac M(x) \Psi(x) . Here, \hbar is Planck's constant divided by 2π, and ''m'' is the
electron mass The electron mass (symbol: ''m''e) is the mass of a stationary electron, also known as the invariant mass of the electron. It is one of the fundamental constants of physics. It has a value of about or about , which has an energy-equivalent of a ...
.) The image PE is usually combined with terms relating to an applied
electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
''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 A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
or into the
semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
: : M(x) = \; h -eFx - e^2/4 \pi \epsilon_0 \epsilon_r x \;. Here, ''e'' is the elementary positive charge, ''ε''0 is the electric constant and ''ε''r is the relative permittivity of the second medium (=1 for
vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
). In the case of a metal–semiconductor junction, this is called a
Schottky barrier A Schottky barrier, named after Walter H. Schottky, is a potential energy barrier for electrons formed at a metal–semiconductor junction. Schottky barriers have rectifying characteristics, suitable for use as a diode. One of the primary char ...
; 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 In solid-state physics, the work function (sometimes spelt workfunction) is the minimum thermodynamic work (i.e., energy) needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface. Here "immediately" m ...
''φ''. This Schottky–Nordheim barrier (SN barrier) has played an important role in the theories of thermionic emission and of
field electron emission Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into a vacuum. However, field emissio ...
. 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 Thermionic emission is the liberation of electrons from an electrode by virtue of its temperature (releasing of energy supplied by heat). This occurs because the thermal energy given to the charge carrier overcomes the work function of the mater ...
". In 1923 Schottky suggested (incorrectly) that the experimental phenomenon then called autoelectronic emission and now called
field electron emission Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into a vacuum. However, field emissio ...
resulted when the barrier was pulled down to zero. In fact, the effect is due to
wave-mechanical tunneling Quantum tunnelling, also known as tunneling ( US) is a quantum mechanical phenomenon whereby a wavefunction can propagate through a potential barrier. The transmission through the barrier can be finite and depends exponentially on the barrier ...
, 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
Schottky barrier A Schottky barrier, named after Walter H. Schottky, is a potential energy barrier for electrons formed at a metal–semiconductor junction. Schottky barriers have rectifying characteristics, suitable for use as a diode. One of the primary char ...
s, 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 The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage ...
. In this context, the metal–semiconductor junction is known as a " Schottky (rectifying) 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.


Awards

He was awarded the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
's
Hughes medal The Hughes Medal is awarded by the Royal Society of London "in recognition of an original discovery in the physical sciences, particularly electricity and magnetism or their applications". Named after David E. Hughes, the medal is awarded with ...
in 1936 for his discovery of the
Schrot effect Walter Hans 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 while working at Siemens, ...
(spontaneous current variations in high-vacuum discharge tubes, called by him the "Schrot effect": literally, the "small shot effect") in thermionic emission and his invention of the screen-grid tetrode and a superheterodyne method of receiving wireless signals. In 1964 he received the
Werner von Siemens Ring The Werner von Siemens Ring (in German orthography, Werner-von-Siemens-Ring) is one of the highest awards for technical sciences in Germany. It has been awarded from 1916 to 1941 and since 1952 about every three years by the foundation ''Stiftung ...
honoring his ground-breaking work on the physical understanding of many phenomena that led to many important technical appliances, among them
tube amplifier A valve amplifier or tube amplifier is a type of electronic amplifier that uses vacuum tubes to increase the amplitude or power of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by sol ...
s and
semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
s.


Controversy

The invention of superheterodyne is usually attributed to
Edwin Armstrong Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American electrical engineer and inventor, who developed FM (frequency modulation) radio and the superheterodyne receiver system. He held 42 patents and received numerous awa ...
. However, Schottky published an article in the
Proceedings of the IEEE The ''Proceedings of the IEEE'' is a monthly peer-reviewed scientific journal published by the Institute of Electrical and Electronics Engineers (IEEE). The journal focuses on electrical engineering and computer science. According to the ''Journa ...
that may indicate he had invented and patented something similar in Germany in 1918. The Frenchman Lucien Lévy had filed a claim earlier than either Armstrong or Schottky, and eventually his patent was recognized in the US and Germany. * 1939: first
p–n junction A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains ...


Legacy

The
Walter Schottky Institute The Walter Schottky Institute (WSI) (german: Walter-Schottky-Institut) is a research center at the Technical University of Munich, dedicated to the physics of semiconductors. Established in 1988, it is located on its Garching campus. It is named ...
for
semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
research and the
Walter Schottky Prize The Walter Schottky Prize is a scientific prize awarded by the Deutsche Physikalische Gesellschaft, German Physical Society for outstanding research work of young academics in the field of solid-state physics. Since 1973 the prize is generally awar ...
are named after him.


Books written by Schottky

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


See also

* Schottky transistor *
Schottky junction solar cell In a basic Schottky-junction (Schottky-barrier) solar cell, an interface between a metal and a semiconductor provides the band bending necessary for charge separation. Traditional solar cells are composed of p-type and n-type semiconductor layer ...
* Surface-barrier transistor


References


External links


Walter Schottky



Walter Schottky Institut
*
Reinhard W. Serchinger: Walter Schottky – Atomtheoretiker und Elektrotechniker.
Sein Leben und Werk bis ins Jahr 1941. Diepholz; Stuttgart; Berlin: GNT-Verlag, 2008.
Schottky's math genealogy
{{DEFAULTSORT:Schottky, Walter H. Semiconductor physicists 1886 births 1976 deaths German electrical engineers 20th-century German physicists Humboldt University of Berlin alumni Werner von Siemens Ring laureates University of Rostock faculty 20th-century German inventors German expatriates in Switzerland