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what is semiconductor?
Overview
Semiconductors are very similar to insulators. The two categories of
solids differ primarily in that insulators have larger band gaps
energies that electrons must acquire to be free to flow. In
semiconductors at room temperature, just as in insulators, very few
electrons gain enough thermal energy to leap the band gap, which is
necessary for conduction. For this reason, pure semiconductors and
insulators, in the absence of applied fields, have roughly similar
electrical properties. The smaller bandgaps of semiconductors,
however, allow for many other means besides temperature to control
their electrical properties.
Semiconductors' intrinsic electrical properties are very often
permanently modified by introducing impurities, in a process known as
doping. Usually it is reasonable to approximate that each impurity
atom adds one electron or one "hole" (a concept to be discussed
later) that may flow freely. Upon the addition of a sufficiently
large proportion of dopants, semiconductors conduct electricity
nearly as well as metals. The junctions between regions of
semiconductors that are doped with different impurities contain
built-in electric fields, which are critical to semiconductor device
operation.
In addition to permanent modification through doping, the electrical
properties of semiconductors are often dynamically modified by
applying electric fields. The ability to control conductivity in
small and well-defined regions of semiconductor material, statically
through doping and dynamically through the application of electric
fields, has led to the development of a broad array of semiconductor
devices, like transistors. Semiconductor devices with dynamically
controlled conductivity are the building blocks of integrated
circuits, like the microprocessor. These "active" semiconductor
devices are combined with simpler passive components, such as
semiconductor capacitors and resistors, to produce a variety of
electronic devices.
In certain semiconductors, when electrons fall from the conduction
band to the valence band (the energy levels above and below the band
gap), they often emit light. This photoemission process underlies the
light-emitting diode (LED) and the semiconductor laser, both of which
are tremendously important commercially. Conversely, semiconductor
absorption of light in photodetectors excites electrons from the
valence band to the conduction band, facilitating reception of fiber
optic communications, and providing the basis for energy from solar
cells.
Semiconductors may be elemental materials, such as silicon, compound
semiconductors such as gallium arsenide, or alloys, such as silicon
germanium or aluminium gallium arsenide.
Energy-momentum dispersion
In the preceding description an important fact is ignored for the sake
of simplicity: the dispersion of the energy. The reason that the
energies of the states are broadened into a band is that the energy
depends on the value of the wave vector, or k-vector, of the
electron. The k-vector, in quantum mechanics, is the representation
of the momentum of a particle. The E-k relationship varies from
material to material.
The effective mass is important as it effects many of the
electrical properties of the semiconductor, such as the electron or
hole mobility, which in turn influences the diffusivity of the charge
carriers and the electrical conductivity of the semiconductor.
Typically the effective mass of electrons and holes are different.
This affects the relative performance of p-channel and n-channel
IGFETs, for example (Muller & Kamins 1986:427).
The top of the valence band and the bottom of the conduction band
might not occur at that same value of k. Materials with this
situation, such as silicon and germanium, are known as indirect
bandgap materials. Materials in which the band extrema are aligned in
k, for example gallium arsenide, are called direct bandgap
semiconductors. Direct gap semiconductors are particularly important
in optoelectronics because they are much more efficient as light
emitters than indirect gap materials.
lima
electronics(Shenzhen)ltd
we are one of the leading agent in China who specialize in the
distribution of international well-known power module
compared with our competitors, we're famous for the upstanding
reputation and high quality of business service
about us
Founded in july 1997, lima electronics mianly work on the sales of
power module, fixing eyes on the market of the industrical line such
as transducerelectric welding machine and USP ect.We
chronically offer IGBTIGCTGTRIPMPIM
SCR rectifier bridge fast recovery
diodes soft recovery diodes fast Fuse ect with the
international well-known brand ,which are producted by
AmericaJapanGermanEnglandSpainSwitzerland
and ect.
support Mfg
1.MITSUBISHI 2.FUJI 3.TOSHIBA
4.SANREX 5.SANKEN 6.HITACHI
7.SEMIKRON 8.SIEMENS 9.IXYS
10.IR 11.EUPEC 12.INFINEON
13.FAIRCHILD 14.TYCO 15.MOTOEOLA
16.SHINDENGEN 17.WESTCODE 18.HINODE
19.BUSSMANN 20.CATELEC 21.MAXIX
22.ABB 23.APT 24.OMRON
25.VICOR 26.LAMBDA 27.COSEL
28.TDK 29.ASTEC 30.LUCENT
31.PRX 32.GOULD 33.FERRAZ
34.SIRECT 35.DYNEX 36.Fine SPN
products:IGBTIGCTGTRIPMPIM
SCR rectifier bridge fast recovery
diodes soft recovery diodesfast Fuse.
ĆĆĆPlease feel free to contact
us!ĆĆĆ
CONTACT ME: Mr zhou/Wendy(miss zhou)
ICQ:381-125-865
MSN: sz-lima@hotmail.com
QQ :173943820
Tel: 86-755-88364656
Fax: 86-755-88364656
E-mail: lima003@21cn.com
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Overview
Semiconductors are very similar to insulators. The two categories of
solids differ primarily in that insulators have larger band gaps
energies that electrons must acquire to be free to flow. In
semiconductors at room temperature, just as in insulators, very few
electrons gain enough thermal energy to leap the band gap, which is
necessary for conduction. For this reason, pure semiconductors and
insulators, in the absence of applied fields, have roughly similar
electrical properties. The smaller bandgaps of semiconductors,
however, allow for many other means besides temperature to control
their electrical properties.
Semiconductors' intrinsic electrical properties are very often
permanently modified by introducing impurities, in a process known as
doping. Usually it is reasonable to approximate that each impurity
atom adds one electron or one "hole" (a concept to be discussed
later) that may flow freely. Upon the addition of a sufficiently
large proportion of dopants, semiconductors conduct electricity
nearly as well as metals. The junctions between regions of
semiconductors that are doped with different impurities contain
built-in electric fields, which are critical to semiconductor device
operation.
In addition to permanent modification through doping, the electrical
properties of semiconductors are often dynamically modified by
applying electric fields. The ability to control conductivity in
small and well-defined regions of semiconductor material, statically
through doping and dynamically through the application of electric
fields, has led to the development of a broad array of semiconductor
devices, like transistors. Semiconductor devices with dynamically
controlled conductivity are the building blocks of integrated
circuits, like the microprocessor. These "active" semiconductor
devices are combined with simpler passive components, such as
semiconductor capacitors and resistors, to produce a variety of
electronic devices.
In certain semiconductors, when electrons fall from the conduction
band to the valence band (the energy levels above and below the band
gap), they often emit light. This photoemission process underlies the
light-emitting diode (LED) and the semiconductor laser, both of which
are tremendously important commercially. Conversely, semiconductor
absorption of light in photodetectors excites electrons from the
valence band to the conduction band, facilitating reception of fiber
optic communications, and providing the basis for energy from solar
cells.
Semiconductors may be elemental materials, such as silicon, compound
semiconductors such as gallium arsenide, or alloys, such as silicon
germanium or aluminium gallium arsenide.
Energy-momentum dispersion
In the preceding description an important fact is ignored for the sake
of simplicity: the dispersion of the energy. The reason that the
energies of the states are broadened into a band is that the energy
depends on the value of the wave vector, or k-vector, of the
electron. The k-vector, in quantum mechanics, is the representation
of the momentum of a particle. The E-k relationship varies from
material to material.
The effective mass is important as it effects many of the
electrical properties of the semiconductor, such as the electron or
hole mobility, which in turn influences the diffusivity of the charge
carriers and the electrical conductivity of the semiconductor.
Typically the effective mass of electrons and holes are different.
This affects the relative performance of p-channel and n-channel
IGFETs, for example (Muller & Kamins 1986:427).
The top of the valence band and the bottom of the conduction band
might not occur at that same value of k. Materials with this
situation, such as silicon and germanium, are known as indirect
bandgap materials. Materials in which the band extrema are aligned in
k, for example gallium arsenide, are called direct bandgap
semiconductors. Direct gap semiconductors are particularly important
in optoelectronics because they are much more efficient as light
emitters than indirect gap materials.
lima
electronics(Shenzhen)ltd
we are one of the leading agent in China who specialize in the
distribution of international well-known power module
compared with our competitors, we're famous for the upstanding
reputation and high quality of business service
about us
Founded in july 1997, lima electronics mianly work on the sales of
power module, fixing eyes on the market of the industrical line such
as transducerelectric welding machine and USP ect.We
chronically offer IGBTIGCTGTRIPMPIM
SCR rectifier bridge fast recovery
diodes soft recovery diodes fast Fuse ect with the
international well-known brand ,which are producted by
AmericaJapanGermanEnglandSpainSwitzerland
and ect.
support Mfg
1.MITSUBISHI 2.FUJI 3.TOSHIBA
4.SANREX 5.SANKEN 6.HITACHI
7.SEMIKRON 8.SIEMENS 9.IXYS
10.IR 11.EUPEC 12.INFINEON
13.FAIRCHILD 14.TYCO 15.MOTOEOLA
16.SHINDENGEN 17.WESTCODE 18.HINODE
19.BUSSMANN 20.CATELEC 21.MAXIX
22.ABB 23.APT 24.OMRON
25.VICOR 26.LAMBDA 27.COSEL
28.TDK 29.ASTEC 30.LUCENT
31.PRX 32.GOULD 33.FERRAZ
34.SIRECT 35.DYNEX 36.Fine SPN
products:IGBTIGCTGTRIPMPIM
SCR rectifier bridge fast recovery
diodes soft recovery diodesfast Fuse.
ĆĆĆPlease feel free to contact
us!ĆĆĆ
CONTACT ME: Mr zhou/Wendy(miss zhou)
ICQ:381-125-865
MSN: sz-lima@hotmail.com
QQ :173943820
Tel: 86-755-88364656
Fax: 86-755-88364656
E-mail: lima003@21cn.com
-------------= Posted from Ugroups.com =-------------
---= Fast & Free Web Portal to Usenet Newsgroups =---
-------------= http://www.ugroups.com/ =-------------