Walter Hermann Schottky (23 July 1886,
ZürichZurich is the largest city in Switzerland and the capital of the canton of Zurich. It is located in central Switzerland at the northwestern tip of Lake Zurich...
, Switzerland – 4 March 1976,
PretzfeldPretzfeld is a municipality in the district of Forchheim in Bavaria in Germany....
, West Germany) 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 tubeIn electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
in 1915 and the
pentodeA pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube , which was invented by the Dutchman Bernhard D.H. Tellegen in 1926...
in 1919 while working at
SiemensSiemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....
, and later made many significant contributions in the areas of semiconductor devices, technical physics and technology.
Education
He graduated from the Steglitz Gymnasium, Berlin, Germany in 1904. He obtained his BS in
PhysicsPhysics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, at the University of Berlin in 1908. He obtained his PhD in Physics at the University of Berlin in 1912 under
Max PlanckMax Karl Ernst Ludwig Planck, ForMemRS, was a German physicist who actualized the quantum physics, initiating a revolution in natural science and philosophy. He is regarded as the founder of the quantum theory, for which he received the Nobel Prize in Physics in 1918.-Life and career:Planck came...
and
Heinrich RubensHeinrich Rubens was a German physicist.He played a direct role in the genesis of the quantum theory, providing the experimental results that pushed Max Planck to provide the first quantum hypothesis.He also combined scientific ideas to create the Rubens' tube.-External links:*...
, with a thesis entitled:
Zur relativtheoretischen Energetik und Dynamik.
Career
His postdoctoral period was spent at University of Jena (1912–14). He then lectured at the
University of WürzburgThe University of Würzburg is a university in Würzburg, Germany, founded in 1402. The university is a member of the distinguished Coimbra Group.-Name:...
(1919–23). He became Professor of Theoretical Physics,
University of RostockThe University of Rostock is the university of the city Rostock, in the German state of Mecklenburg-Vorpommern.Founded in 1419, it is the oldest and largest university in continental northern Europe and the Baltic Sea area...
(1923–27). For two periods he worked at the Siemens Research laboratories (1914–19, 1927–58).
Major scientific achievements
Possibly, in retrospect, Schottky's most important scientific achievement was to develop (in 1914) the well-known classical formula, now written -
q2/16π
ε0x, for the interaction energy between a point
chargeElectric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
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 KelvinWilliam Thomson, 1st Baron Kelvin OM, GCVO, PC, PRS, PRSE, was a mathematical physicist and engineer. At the University of Glasgow he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging...
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-
semiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
interface from the inside. (This
M(
x) is the quantity that appears when the one-dimensional, one-particle,
Schrödinger equationThe Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....
is written in the form
Here,
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 fieldIn physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
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
vacuumIn everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
or into the
semiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
:
Here,
e is the
elementary positive chargeThe elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...
,
ε0 is the
electric constantThe physical constant ε0, commonly called the vacuum permittivity, permittivity of free space or electric constant is an ideal, physical constant, which is the value of the absolute dielectric permittivity of classical vacuum...
and
εr is the relative permittivity of the second medium (=1 for
vacuumIn everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
). In the case of a
metal-semiconductor junctionIn solid-state physics, a metal–semiconductor junction is a type of junction in which a metal comes in close contact with a semiconductor material...
, this is called a
Schottky barrierA Schottky barrier, named after Walter H. Schottky, is a potential barrier formed at a metal–semiconductor junction which has rectifying characteristics, suitable for use as a diode...
; 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 functionIn solid-state physics, the work function is the minimum energy needed to remove an electron from a solid to a point immediately outside the solid surface...
φ.
This Schottky–Nordheim barrier (SN barrier) has played in important role in the theories of
thermionic emissionThermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
and of field electron emission. Applying the field causes lowering of the barrier, and thus enhances the emission current in
thermionic emissionThermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
. This is called the "
Schottky effectThermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
", and the resulting emission regime is called "
Schottky emissionThermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
".
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 tunnelingQuantum tunnelling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount. This plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the sun, and has important...
, 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 barrierA Schottky barrier, named after Walter H. Schottky, is a potential barrier formed at a metal–semiconductor junction which has rectifying characteristics, suitable for use as a diode...
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 diodeThe Schottky diode is a semiconductor diode with a low forward voltage drop and a very fast switching action...
. In this context, the
metal-semiconductor junctionIn solid-state physics, a metal–semiconductor junction is a type of junction in which a metal comes in close contact with a semiconductor material...
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 SocietyThe Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
's
Hughes medalThe 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 a gift of £1000. The medal was first awarded in 1902 to...
in 1936 for his discovery of the Schrot effect (spontaneous current variations in high-vacuum discharge tubes, called by him the "Schrot effect": literally, the "small shot effect") in
thermionic emissionThermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and...
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 honoring his ground-breaking work on the physical understanding of many phenomena that led to many important technical appliances, among them tube amplifiers and
semiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s.
Controversy
The invention of superheterodyne is usually attributed to
Edwin ArmstrongEdwin Howard Armstrong was an American electrical engineer and inventor. Armstrong was the inventor of modern frequency modulation radio....
. However, Schottky published an article in Proc. IRE that he had also invented something similar.
- 1939: first p-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...
Personal life
His father was
mathematicianA mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....
Friedrich Hermann Schottky (1851–1935). His wife was Elizabeth and they had one daughter and two sons. His father was appointed professor of mathematics at the
University of ZurichThe University of Zurich , located in the city of Zurich, is the largest university in Switzerland, with over 25,000 students. It was founded in 1833 from the existing colleges of theology, law, medicine and a new faculty of philosophy....
in 1882, and he was born 4 years later. The family then moved back to Germany in 1892, where his father took up an appointment at the University of Marburg.