Semiconductors as a special class of substances have been known since the late XIX
century, only the development of solid-state theory led to an understanding of their feature
long before that were found:
1. The effect of rectification at metal-semiconductor contact
2. photo conductivity.
Constructed the first devices based on them.
Losev (1923) demonstrated the possibility of using contacts
semiconductor-metal for the amplification and generation of oscillations (crystalline
detector). However, in later years crystal detectors were
superseded vacuum tubes and only in the early 50 - ies with the opening
transistors (USA 1949) began widespread use of semiconductors
(mainly germanium and silicon in electronics. At the same time
began an intensive study of the properties of semiconductors, helped
improved methods of purification of crystals and their doping (introduction to
Semiconductor certain impurities).
In the USSR, the study of semiconductors began in the late 20 - ies under
leadership AF Ioffe Physico-Technical Institute of the USSR.
Interest in the optical properties of semiconductors grew makes it possible for the opening
stimulated emission in semiconductors, resulting in the creation
semiconductor lasers, first on the p - n - transition, and then
heterojunctions.
NOTE: In more recent widespread devices based on
Semiconductor action. These substances began to study relatively recently,
but without them can not do any modern electronics or
medicine, nor many other sciences.
properties of Semiconductors
Semiconductors - a class of compounds characterized by the values
specific electric conductivity (which lies in the range between the specific
Electrical conductivity of metals and dielectrics good, that is, these substances
can not be classified as a dielectric (because they are not good
insulators) and to metals (conductors are not good
electrical current). For semiconductors, for example, include such substances
germanium, silicon, selenium, tellurium, and some oxides, sulfides, and
metal alloys.
Semiconductors long time did not attract much attention of scientists and
engineers. One of the first systematic studies of physical
properties of semiconductors prominent Soviet physicist Abram Ioffe.
He found that semiconductors - a special class of crystals with many
remarkable properties:
1) With increasing temperature, the resistivity semiconductors
decreases, unlike metals, have a resistivity which
raising the temperature increases. Moreover, usually in a wide
the temperature increase that happens eksponentsionalno:
(= (O (exp. (- (A / kT)
where (a - the so-called activation energy of conductivity,
(o - coefficient of temperature-dependent
The resistivity of the semiconductor crystals can also be reduced
when exposed to light or strong electric fields.
2) Property unilateral conductivity of contact between two semiconductors.
This property is used to create a variety of
semiconductor devices: diodes, transistors, thyristors and others.
3) Contact various semiconductors under certain conditions when illuminated
or heating are the sources of photo - e. d. s. resp
thermo - e. d. s.
The structure of semiconductors and how they work.
As mentioned, semiconductors are a special class
crystals. Valence electrons form a correct covalent bonds,
schematically. Such an ideal semiconductor
did not conduct an electric current (in the absence of light and
radiation exposure).
As in nonconductors electrons in semiconductors associated with
atoms, but this relationship is very fragile. With increasing temperature,
(T> 0 K), light or electron irradiation connection can rupture that
lead to a separation of the electron from the atom. Such an electron is
current carrier. The higher the temperature of the semiconductor, the higher the concentration
conduction electrons, hence the lower the resistivity.
Thus, a decrease in heat resistance semiconductor
due to the increase in the concentration of charge carriers in it.
Unlike conductors carriers in semiconductor materials
may be not only electrons but also a "hole". With the loss of one electron
of semiconductor atoms in its orbit remains empty place- "hole" in the
Effects of electric field on the crystal "hole" as a positive charge
moves in the direction of the vector E, which is due to the fact
break some links and other restoration. "Holes" can be roughly considered
particle carrying a positive charge.
Impurity conductivity.
The same semiconductor has either an electron or hole
conductivity - it depends upon the chemical composition of the impurities introduced.
Impurities have a strong impact on the electrical conductivity
semiconductor:
For example, thousandths of a percent of the impurities can be in the hundreds of thousands of times
reduce their resistance. This fact, on one hand, indicates
possibility of changing the properties of semiconductors on the other hand, it
evidence of the difficulties in the manufacture of semiconductor technology
materials with desired properties.
Considering the mechanism of the effect of impurities on the electrical conductivity
semiconductors, two cases should be considered:
Electronic conductivity.
Addition of germanium in the impurities-rich electrons, for example arsenic or
antimony, allows to obtain an electronically conductive semiconductor or
semiconductor n - type (from the Latin word "negativus" -
"Negative").
One
arsenic valence electrons is not involved in relationships with other atoms. at
raising the temperature of the electron can be detached from the atom and
thereby creating electronic conductivity.
Impurities constitute such electro conductivity called donor.
hole conduction
Addition of the same aluminum, germanium, gallium or indium creates crystal
excess holes. Then, the semiconductor will have a hole conductivity -
semiconductor p - type.
Electrical conductivity of the p-type impurity atoms having a smaller sozdetsya
the number of valence electrons than the basic atoms. schematically
shows the electronic communication of germanium doped with boron. At 0 K, all communications
Staffing, only boron is not enough of a connection. however
with increasing temperature, boron may saturate your connection due to the electrons
neighboring atoms.
These impurities are called acceptor.
liquid semiconductors
Melting-crystal semiconductor accompanied many sharp
increase their electrical conductivity values of Q to typically for metals
However, for a number of semiconductors (eg HgSe, HgTe and. T. D.)
characterized by the maintenance or reduction of Q during melting and preservation
semiconductors in the temperature dependence Q (Electrical conductivity.
Some liquid semiconductor at higher temperatures lose
semi conducting properties and acquire metal . Alloys as Te - Se, Se-rich behave differently, their
Electrical conductivity is purely semi-conducting nature.
In a liquid semiconductor band-gap role is played by the energy
near the minimum of the density of states in the energy spectrum of electrons.
At sufficiently deep minimum in the vicinity zone appears almost
localized states of the charge carriers with low mobility
(pseudo-gap). If the temperature rises there is a "collapse"
pseudo-gap liquid semiconductor is converted into the metal.
Using semiconductors.
The most important technique for semiconductor devices - diodes, transistors,
thyristors based on the use of materials with excellent electronic
or p-type conductivity.
The widespread use of semiconductors began relatively recently, and now
they got a very extensive use. They convert light and heat
energy into electrical energy and vice versa, using electricity create heat
and cold. Semiconductor devices can be found in the usual radio
and maser - laser in the tiny atomic battery and
microprocessors.
Engineers can not do without semi conducting rectifiers
switches and amplifiers. Replacement lamp semiconductor equipment
allowed dozens of times to reduce the size and weight of electronic devices,
reduce the consumption of power and dramatically increase reliability.
https://www.youtube.com/watch?v=QYhVOMaeP4s
ReplyDelete