Who invented semiconductor?

Question

Aliens?

Answer 1

Karl Braun, in Germany, 1874, discovered the galena chrstal rectified alternating current. This was the basis of the cat's whisker detector in crystal radio sets in the early 1900s. Perhaps this was the first semiconductor used for electrical purposes.

On the other hand, carborundum is another 19th century semiconductor device but I don't know who invented that use or when.

Selenium rectifiers were in common use in the 1950s

Noyce is credited with a development of the integrated circuit in 1961---Kilby filed the patent for the first integrated circuit in 1959

Answer 2

On 22 December 1947 William Shockley, John Bardeen and Walter Brattain succeeded in building the first practical point-contact transistor at Bell Labs. This work followed from their war-time efforts to produce extremely pure germanium "crystal" mixer diodes, used in radar units as a frequency mixer element in microwave radar receivers. Early tube-based technology did not switch fast enough for this role, leading the Bell team to use solid state diodes instead. With this knowledge in hand they turned to the design of a triode, but found this was not at all easy. Bardeen eventually developed a new branch of surface physics to account for the "odd" behaviour they saw, and Bardeen and Brattain eventually succeeded in building a working device.

Bell Telephone Laboratories needed a generic name for the new invention: "Semiconductor Triode", "Solid Triode", "Surface States Triode", "Crystal Triode" and "Iotatron" were all considered, but "transistor," coined by John R. Pierce, won an internal ballot. The rationale for the name is described in the following extract from the company's Technical Memoranda calling

Answer 3

Somebody at Bell Labs invented the transistor, while trying to invent a better diode.

Answer 4

Al Gore before he invented the internet.

Answer 5

I don't know who invented them but my stocks are sure in the shi*tter!

Robert Noyce and Jack Kilby co-invented the integrated circuit in 1959

Answer 6

Robert N. Noyce

Answer 7

Al Gore's HALF brother

Answer 8

semiwhat?

YEAH ur absolutely right.

ALIENS.

Answer 9

A semiconductor is a material with an electrical conductivity that is intermediate between that of an insulator and a conductor.




Contents [hide]
1 Explanation
2 How semiconductors work
3 Fundamental semiconductor physics
3.1 Band structure of a semiconductor
3.2 Electron-hole pairs
4 Doping of semiconductors
4.1 Intrinsic and extrinsic semiconductors
4.2 N-type doping
4.3 P-type doping
4.4 Carrier concentrations
5 P-N junctions
6 Required purity and perfection of semiconductor materials
7 See also
8 References
9 External links



[edit]
Explanation
A semiconductor behaves as an insulator at very low temperatures, and has an appreciable electrical conductivity at room temperature although much lower conductivity than a conductor. Commonly used semiconducting materials are silicon, germanium, gallium arsenide, indium phosphide, and mercury cadmium telluride.

A semiconductor can be distinguished from a conductor by the fact that, at absolute zero, the uppermost filled electron energy band is completely filled in a semiconductor, but only partially filled in a conductor.

The distinction between a semiconductor and an insulator is slightly more arbitrary. A semiconductor has a band gap which is small enough such that its conduction band is appreciably thermally populated with electrons at room temperature, whilst an insulator has a band gap which is too wide for there to be appreciable thermal electrons in its conduction band at room temperature.

[edit]
How semiconductors work
Operationally, transistors and vacuum tubes have similar functions; they both control the flow of electrical current.


An absolutely pure silicon crystal is also an insulator, but when an impurity e.g. arsenic is added (called doping) in quantities minute enough not to completely disrupt the regularity of the crystal lattice, it donates free electrons and enables conduction. This is because arsenic atoms have five electrons in their outer shells while silicon atoms have only four. Conduction is possible because a mobile carrier of charge has been introduced, in this case creating n-type silicon ("n" for negative. The electron has a negative charge).

Alternatively, silicon can be doped with boron to make p-type silicon which also conducts. Because boron has only three electrons in its outer shell another kind of charge carrier, called a "hole", is formed in the silicon crystal lattice.

In a vacuum tube, on the other hand, the charge carriers (electrons) are emitted by thermionic emission from a cathode heated by a wire filament. Therefore, vacuum tubes cannot generate holes (positive charge carriers).

Note that charge carriers of the same polarity repel one another so that, in the absence of any force, they are distributed evenly throughout the semiconductor material. However, in an unpowered bipolar transistor (or junction diode) the charge carriers tend to migrate towards a P/N junction, being attracted by their opposite charge carriers on the other side of the junction.

Increasing the doping level increases the semiconductor conductivity, providing that the crystal lattice, overall, remains intact. In a bipolar transistor the emitter has a higher doping level than the base. The ratio of emitter/base doping levels is one of the main factors that dictates the junction transistor's current gain.

The level of doping is extremely low: in the order of parts per one hundred million, and this is the key to semiconductor operation. In metals, the carrier population is extremely high; one charge-carrier per atom. In metals, in order to convert a significant volume of the material into an insulator, the charge carriers must be swept out by applying a voltage. In metals this value of voltage is astronomical; more than enough to destroy the metal before it converts to an insulator. But in lightly-doped semiconductors there is only one mobile charge carrier per millions or more atoms. The level of voltage required to sweep so few charge-carriers out of a significant volume of the material is easily reached. In other words, the electricity in metals is incompressible, like a fluid, while in semiconductors behaves as a compressible gas. Doped semiconductors can be rapidly changed into insulators, while metals cannot.

The above explains conduction in a semiconductor by charge carriers, either electrons or holes, but the essence of bipolar transistor action is the way that electrons/holes seemingly make a prohibited leap across the insulating depletion zone in the reverse-biased base/collector junction under control of the base/emitter voltage. Although a transistor may seem like two interconnected diodes, a bipolar transistor cannot be made simply by connecting two discrete junction diodes together. To produce bipolar transistor action they need to be fabricated on the same crystal, and physically sharing a common and extremely thin base region.

[edit]
Fundamental semiconductor physics
[edit]
Band structure of a semiconductor

Band structure of a semiconductor showing a full valence band and an empty conduction band. The Fermi level lies within the bandgapIn the parlance of solid-state physics, semiconductors (and insulators) are defined as solids in which at absolute zero (0 K), the uppermost band of occupied electron energy states, known as the valence band, is completely full. Under absolute zero conditions, the Fermi energy, or Fermi level, can be thought of as the energy up to which available electron states are occupied.

At room temperatures, there is some smearing of the energy distribution of the electrons, such that a small, but not insignificant number have enough energy to cross the energy band gap into the conduction band. These electrons which have enough energy to be in the conduction band have broken free of the covalent bonds between neighbouring atoms in the solid, and are free to move around, and hence conduct charge. The covalent bonds from which these excited electrons have come now have missing electrons, or holes which are free to move around as well. (The holes themselves don't actually move, but a neighbouring electron can move to fill the hole, leaving a hole at the place it has just come from, and in this way the holes appear to move.)

It is an important distinction between conductors and semiconductors that, in semiconductors, movement of charge (current) is facilitated by both electrons and holes. Contrast this to a conductor where the Fermi level lies within the conduction band, such that the band is only half filled with electrons. In this case, only a small amount of energy is needed for the electrons to find other unoccupied states to move into, and hence for current to flow.

The ease with which electrons in a semiconductor can be excited from the valence band to the conduction band depends on the band gap between the bands, and it is the size of this energy bandgap that serves as an arbitrary dividing line between semiconductors and insulators. Materials with a bandgap energy of less than about 3 electronvolts (eV) are generally considered semiconductors, while those with a greater bandgap energy are considered insulators.

The current-carrying electrons in the conduction band are known as "free electrons", although they are often simply called "electrons" if context allows this usage to be clear. The holes in the valence band behave very much like positively-charged counterparts of electrons, and they are usually treated as if they are real charged particles.

It is interesting to note that the reason semiconductors work is a direct result of quantum physics, in specific the Pauli exclusion principle. This principle states that no two particles can exist in the same state at the same time. Electrons and holes both behave in this way, and the entire electron-hole state is forced to follow certain energy distribution statistics, which basically mean that at any given temperature the distribution of free electrons and holes are statistically determined and predictable. This also means that the conductivity of a semiconductor has a heavy temperature dependency, as a semiconductor operating at very low temperatures (-100°C or so) will have significantly fewer available free electrons and holes able to do the work. If you cool an IC down cold enough, the semiconductor will go intrinsic and all electrical signals will stop. (You would think that heating up the semiconductor has the opposite effect, but there are lots of other problems that happen at high temperatures, including loss of semiconducting properties due to too much free energy, so there is always a happy middle where the semiconductor wants to play!)

[edit]
Electron-hole pairs
When ionizing radiation strikes a semiconductor, it will often excite an electron out of its energy level and consequently leave a hole. This process is known as electron-hole pair generation. A useful concept is the exciton which describes the electron and hole being bound together into a quasiparticle. The details of the specific processes through which electron-hole pairs are created are not well known, however, it is known that the average energy needed to create an electron-hole pair at a given temperature is dependent of the type and the energy of the ionizing radiation. In silicon, this energy is equal to 3.62 eV at room temperature and 3.72 eV at 80 K.

[edit]
Doping of semiconductors
One of the main reasons that semiconductors are useful in electronics is that their electronic properties can be greatly altered in a controllable way by adding small amounts of impurities. These impurities are called dopants.

Heavily doping a semiconductor can increase its conductivity by a factor greater than a billion. In modern integrated circuits, for instance, heavily-doped polycrystalline silicon is often used as a replacement for metals.

[edit]
Intrinsic and extrinsic semiconductors
An intrinsic semiconductor is a semiconductor which is pure enough that the impurities in it do not appreciably affect its electrical behavior. In this case, all carriers are created by thermally or optically excited electrons from the full valence band into the empty conduction band. Thus equal numbers of electrons and holes are present in an intrinsic semiconductor. Electrons and holes flow in opposite directions in an electric field, though they contribute to current in the same direction since they are oppositely charged. Hole current and electron current are not necessarily equal in an intrinsic semiconductor, however, because electrons and holes have different effective masses (crystalline analogues to free inertial masses).

The concentration of carriers in an intrinsic semiconductor is strongly dependent on the temperature. At low temperatures, the valence band is completely full, making the material an insulator (see electrical conduction for more information). Increasing the temperature leads to an increase in the number of carriers and a corresponding increase in conductivity. This principle is used in thermistors. This behavior contrasts sharply with that of most metals, which tend to become less conductive at higher temperatures due to increased phonon scattering.

An extrinsic semiconductor is a semiconductor that has been doped with impurities to modify the number and type of free charge carriers present.

A semiconductor which is doped to such high levels that the dopant atoms are an appreciable fraction of the semiconductor atoms is called degenerate. A degenerate semiconductor acts more like a conductor than a semiconductor.

[edit]
N-type doping
The purpose of n-type doping is to produce an abundance of mobile or "carrier" electrons in the material. To help understand how n-type doping is accomplished, consider the case of silicon (Si). Si atoms have four valence electrons, each of which is covalently bonded with one of four adjacent Si atoms. If an atom with five valence electrons, such as those from group 15 (a.k.a. group V) of the periodic table (e.g. phosphorus (P), arsenic (As), or antimony (Sb)), is incorporated into the crystal lattice in place of a Si atom, then that atom will have four covalent bonds and one unbonded electron. This extra electron is only weakly bound to the atom and can easily be excited into the conduction band. At room temperatures, virtually all such electrons are excited into the conduction band. Since excitation of these weakly bound electrons does not result in the formation of a hole, the number of electrons in such a material far exceeds the number of thermally generated holes. In this case the electrons are the majority carriers and the holes are the minority carriers. Because the five-electron atoms have an extra electron to "donate", they are called donor atoms. Note that each movable electron within the semiconductor is never far from an immobile positive dopant ion, and the n-doped material normally has a net electric charge of zero.

[edit]
P-type doping
The purpose of p-type doping is to create an abundance of holes. In the case of silicon, a trivalent atom (an atom in Group III, such as boron) is substituted into the crystal lattice. The result is that one electron is missing from one of the four covalent bonds normal for the silicon lattice. Thus the dopant atom can accept an electron from a neighboring atom's covalent bond to complete the fourth bond. Such dopants are called acceptors. The dopant atom accepts an electron, causing the loss of one bond from the neighboring atom and resulting in the formation of a "hole". Each hole is associated with a nearby negative-charged dopant ion, and the semiconductor remains electrically neutral as a whole. However, once each hole has wandered away into the lattice, one proton in the atom at the hole's location will be "exposed" and no longer cancelled by an electron. For this reason a hole behaves as a quantity of positive charge. When a sufficiently large number of acceptor atoms are added, the holes greatly outnumber the thermally-excited electrons. Thus, the holes are the majority carriers, while electrons are the minority carriers in P-type materials. Blue diamonds (Type IIb), which contain boron (B) impurities, are an example of a naturally occurring P-type semiconductor.

[edit]
Carrier concentrations
When a semiconductor is doped, its majority carrier concentration exceeds the intrinsic carrier concentration by a factor that is dependent on the doping level. However, the product of the majority and minority carrier concentrations continues to be equal to the square of the intrinsic carrier concentration.



where Ni is the intrinsic carrier concentration.

Consider an intrinsic semiconductor at a temperature such that the carrier concentrations of holes and electrons are each 1013/cm3. From the above equation, it can be seen that:



If this semiconductior is then n-doped to 1016/cm3, then the hole concentration will be 1010/cm3. It also follows from this that minority carrier concentrations in doped semiconductors are dependent on temperature to the square of the extent that carrier concentrations in intrinsic semiconductors are, since the majority carrier concentration is effectively fixed at the doping level.

[edit]
P-N junctions
A p-n junction may be created by doping adjacent regions of a semiconductor with p-type and n-type dopants. If a positive bias voltage is placed on the p-type side, the dominant positive carriers (holes) are pushed toward the junction. At the same time, the dominant negative carriers (electrons) in the n-type material are attracted toward the junction. Since there is an abundance of carriers at the junction, the junction behaves as a conductor, and the voltage placed across the junction produces a current. As the clouds of holes and electrons are forced to overlap, electrons fall into holes and become part of the population of immobile covalent bonds. However, if the bias polarity is reversed, the holes and electrons are pulled away from the junction. Since only very few new electron/hole pairs are created at the junction, the existing mobile carriers are swept away to leave a depletion zone; a region of relatively non-conducting silicon. The reverse bias voltage will produce only a very low current across the junction. The p-n junction is the basis of an electronic device called a diode, which allows electric charges to flow in only one direction. Similarly, a third semiconductor region can be doped n-type or p-type to form a three-terminal device, such as the bipolar junction transistor (which can be either p-n-p or n-p-n).

When an electron-hole pair is created in the depletion region by ionizing radiation the two liberated charged particles will be swept out of the area. After the electron-hole pair is created in the depletion region, the hole will be swept towards the p-type region by the electric field, and the electron will be swept towards the n-type region by the electric field. The movement of these charge carriers constitutes a small electrical current which can be measured and analyzed.

[edit]
Required purity and perfection of semiconductor materials
Semiconductors with predictable, reliable electronic properties are necessary for mass production. The level of chemical purity needed is extremely high because the presence of impurities even in very small proportions can have large effects on the properties of the material. A high degree of crystalline perfection is also required, since faults in crystal structure (such as dislocations, twins, and stacking faults) interfere with the semiconducting properties of the material. Crystalline faults are a major cause of defective semiconductor devices. The larger the crystal, the more difficult it is to achieve the necessary perfection. Current mass production processes use crystal ingots between four and twelve inches (300 mm) in diameter which are grown as cylinders and sliced into wafers.

Because of the required level of chemical purity, and the perfection of the crystal structure which are needed to make semiconductor devices, special methods have been developed to produce the initial semiconductor material. A technique for achieving high purity includes growing the crystal using the Czochralski process. An additional step that can be used to further increase purity is known as zone refining. In zone refining, part of a solid crystal is melted. The impurities tend to concentrate in the melted region, while the desired material recrystalizes leaving the solid material more pure and with fewer crystalline faults.




[edit]
See also
Semiconductor device fabrication
Semiconductor devices
Transistors
Diodes
Microprocessors
Thermistors
Solar cells
Piezoresistors
Semiconductor materials
Spintronics
Solid state physics
Solid state chemistry
Electrical engineering
Carrier generation and recombination
Conduction band
Effective mass
Electron hole
Electron-hole pair
Exciton
Quantum tunneling
Valence band
Wide bandgap semiconductors
[edit]
References
Yu, Peter Y.; Cardona, Manuel (2004). Fundamentals of Semiconductors : Physics and Materials Properties. Springer. ISBN 3540413235.
Sze, Simon M. (1981). Physics of Semiconductor Devices (2nd ed.). John Wiley and Sons (WIE). ISBN 0471056618.
Turley, Jim (2002). The Essential Guide to Semiconductors. Prentice Hall PTR. ISBN 013046404X.
[edit]
External links
Howstuffworks' semiconductor page
US Navy Electrical Engineering Training Series
NSM-Archive Physical Properties of Semiconductors
Semiconductor Concepts at Hyperphysics
Principles of Semiconductor Devices by Bart Van Zeghbroeck, University of Colorado
Semiconductor OneSource Hall of Fame, Glossary
Britney Spears Guide to Semiconductor Physics semiconductors, pn junctions, heterostructures, semiconductor growth and fabrication, quantum wells and laser physics.
SiliconFarEast.com What is a semiconductor?




General subfields within physics v·d·e

Atomic, molecular, and optical physics | Classical mechanics | Condensed matter physics | Continuum mechanics | Electromagnetism | Special relativity | General relativity | Particle physics | Quantum field theory | Quantum mechanics | Statistical mechanics | Thermodynamics


Retrieved from "http://en.wikipedia.org/wiki/Semiconductor"
Category: Semiconductors

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