Schottky barrier

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Schottky barrier

A Schottky barrier, named after Walter H. Schottky

Walter H. Schottky

Walter Hermann Schottky was a Germany physicist who invented the screen-grid vacuum tube in 1915 and the tetrode in 1919 while working at Siemens AG....
, is a potential barrier formed at a metal

Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
-semiconductor

Semiconductor

A semiconductor is a material that has electrical conductivity between those of a Electrical conductor and an electrical insulation; it can vary over that wide range either permanently or dynamically....
junction which has rectifying characteristics, suitable for use as a diode

Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
. The largest differences between a Schottky barrier and a p-n junction

P-n junction

A p-n junction is a junction formed by combining P-type semiconductor and N-type semiconductor semiconductors together in very close contact.The term junction refers to the region where the two regions of the semiconductor meet....
are its typically lower junction voltage, and decreased (almost nonexistent) depletion width in the metal.

Not all metal-semiconductor junctions form Schottky barriers. A metal-semiconductor junction that does not rectify current is called an ohmic contact

Ohmic contact

An ohmic contact is a region on a semiconductor device that has been prepared so that the Current-voltage characteristic curve of the device is linear and symmetric....
.

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Encyclopedia

A Schottky barrier, named after Walter H. Schottky

Walter H. Schottky

Metal

Semiconductor

Diode

P-n junction

Ohmic contact

An ohmic contact is a region on a semiconductor device that has been prepared so that the Current-voltage characteristic curve of the device is linear and symmetric....
. Rectifying properties depend on the metal's work function

Work function

In 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 ....
, the band gap

Band gap

In solid state physics and related applied fields, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states exist....
of the intrinsic semiconductor, the type and concentration

Concentration

In chemistry, concentration is the measure of how much of a given chemical substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent....
of dopant

Dopant

A dopant, also called doping agent and dope, is an impurity element added to a crystal or semiconductor lattice in low concentrations in order to alter the optical/electrical properties of the semiconductor....
s in the semiconductor, and other factors. Design of semiconductor devices requires familiarity with the Schottky effect to ensure Schottky barriers are not created accidentally where an ohmic connection is desired.

Advantages

Schottky barriers, with their lower junction voltage, find application where a device better approximating an ideal diode is desired. They are also used in conjunction with normal diodes and transistor

Transistor

In electronics, a transistor is a semiconductor device commonly used to Electronic amplifier or switch Electronics signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit....
s, where their lower junction voltage is used for circuit protection (among other things).

Because one of the materials in a Schottky diode is a metal, lower resistance devices are often possible. In addition, the fact that only one type of dopant is needed may greatly simplify fabrication. And because of the low depletion width, Schottky diodes can achieve greater switching speeds than p-n junction diodes, making them appropriate to rectify high frequency signals.

Overall, however, Schottky devices find only limited application compared to other semiconductor technologies.

Devices

A metal-semiconductor junction that forms a Schottky barrier as a device by itself is known as a Schottky diode

Schottky diode

The Schottky diode is a semiconductor diode with a low forward voltage drop and a very fast switching action.The cat's-whisker detectors used in the early days of wireless#History can be considered as primitive Schottky diodes....
.

A bipolar junction transistor

Bipolar junction transistor

A bipolar transistor is a type of transistor. It is a three-terminal device constructed of Doping semiconductor material and may be used in Electronic amplifier or switching applications....
with a Schottky barrier between the base and the collector is known as a Schottky transistor. Because the junction voltage of the Schottky barrier is small, the transistor is prevented from saturating too deeply, which improves the speed when used as a switch. This is the basis for the Schottky and Advanced Schottky TTL

Transistor-transistor logic

File:68k ttl.jpgTransistor?transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor?transistor logic because both the logic gating function and the amplifying function are performed by transistors ....
families, as well as their low power

Electric power

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt .When electric current flows in a circuit, it can transfer energy to do mechanical work or work ....
variants.

A MESFET

MESFET

MESFET stands for MEtal Semiconductor Field Effect Transistor. It is quite similar to a JFET in construction and terminology. The difference is that instead of using a p-n junction for a gate, a Schottky barrier junction is used....
, or Metal-Semiconductor FET

Field effect transistor

The field-effect transistor is a type of transistor that relies on an electric field to control the shape and hence the electrical conductivity of a channel of one type of charge carrier in a semiconductor material....
, is a device similar in operation to the JFET

JFET

The junction gate field-effect transistor is the simplest type of field effect transistor. It can be used as an electronics-controlled switch or as a voltage-controlled Electrical resistance....
, which utilizes a reverse biased Schottky barrier to provide the depletion region. A particularly interesting variant of this device is the HEMT

HEMT

HEMT stands for High Electron Mobility Transistor, and is also called heterostructure FET or modulation-doped FET . A HEMT is a field effect transistor incorporating a junction between two materials with different band gaps as the channel instead of a doped region, as is generally the case for MOSFETs....
, or High Electron Mobility Transistor, which also utilizes a heterojunction

Heterojunction

A heterojunction is the interface that occurs between two layers or regions of dissimilar crystalline semiconductors. These semiconducting materials have unequal band gaps as opposed to a homojunction....
to provide a device with extremely high conductance.

Schottky barriers are commonly used also in semiconductor electrical characterization techniques. In fact, in the semiconductor, a depletion region

Depletion region

In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region, is an insulating region within a conductive, doping semiconductor material where the charge carriers have Diffusion away, or have been forced away by an electric field....
is created by the metal electrons, which "push" away semiconductor electrons (simplification, see depletion region

Depletion region

In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region, is an insulating region within a conductive, doping semiconductor material where the charge carriers have Diffusion away, or have been forced away by an electric field....
article). In the depletion region, dopants remain ionized and give rise to a "space charge" which, in turn, give rise to a capacitance

Capacitance

In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge.Capacitance is also a measure of the amount of electric charge stored for a given electric potential....
of the junction. The metal-semiconductor interface and the opposite boundary of the depleted area act like two capacitor plates, with the depletion region

Depletion region

Dielectric

A dielectric is a nonconducting substance, i.e. an Insulator . The term was coined by William Whewell in response to a request from Michael Faraday....
. By applying a voltage to the junction it is possible to vary the depletion width: if we reverse bias the junction, the dopants electrons will be emitted and pushed away; if we forward bias the junction, the electrons will be captured. By analyzing the emission and capture of electrons by dopants (or, more frequently, by crystallographic defects or dislocations, or other electron traps) is possible to characterize the semiconductor material. The most popular electrical characterization techniques that use this type of junction are DLTS and CV profiling

CV profiling

The "CV", or more correctly "C-V", in C-V profiling, stands for capacitance-voltage, and refers to a technique used for characterization of semiconductor materials and devices....
.

A Schottky barrier carbon nanotube

Carbon nanotube

Carbon nanotubes are allotropes of carbon with a nanostructure that can have a length-to-diameter ratio of up to 28,000,000:1, which is significantly larger than any other material....
FET uses the nonideal contact between a metal and a carbon nanotube (CNT) to form a Schottky barrier that can be used to make Schottky diodes or transistors, or so on. The scaling of semiconductor devices to ever-smaller sizes is rapidly approaching fundamental limits. Carbon nanotubes may become a practical alternative to customary devices due to their small size and unique mechanical and electronic properties.

Schottky barrier

Advantages

Devices

See also

External links