Band gap

In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is often spelled "bandgap".

Related Topics:
Solid state physics - Valence band - Conduction band - Insulator - Semiconductor

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Semiconductor band structureSee electrical conduction and semiconductor for a more detailed description of band structure.

Related Topics:
Electrical conduction - Semiconductor

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An intrinsic (pure) semiconductor's conductivity is strongly dependent on the band gap. The only available carriers for conduction are the electrons which have enough thermal energy to be excited across the band gap, which is defined as the energy level difference between the conduction band and the valence band. From Fermi-Dirac statistics (to be precise the Boltzmann's approximation is actually used), the probability of these excitations occurring is proportional to:

Related Topics:
Conductivity - Fermi-Dirac statistics

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:e^left(rac{-E_g}{kT} ight)

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where:

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:e is the exponential function

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:Eg is the band gap energy

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:k is Boltzmann's constant

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:T is temperature

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Conductivity is undesirable, and larger band gap materials give better performance. In infrared photodiodes, a small band gap semiconductor is used to allow detection of low-energy photons.

Related Topics:
Infrared - Photodiode

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Band gaps

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Common materials at room temperature

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Ge 0.67 eV

Related Topics:
Ge - EV

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InN 0.7 eV

Related Topics:
InN - EV

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InGaN 0.7 - 3.4eV

Related Topics:
InGaN - EV

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Si 1.14 eV

Related Topics:
Si - EV

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InP 1.34 eV

Related Topics:
InP - EV

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GaAs 1.43 eV

Related Topics:
GaAs - EV

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AlGaAs 1.42 - 2.16 eV

Related Topics:
AlGaAs - EV

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AlAs 2.16 eV

Related Topics:
AlAs - EV

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SiC 6H 3.03 eV

Related Topics:
SiC - EV

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SiC 4H 3.28 eV

Related Topics:
SiC - EV

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GaN 3.37 eV

Related Topics:
GaN - EV

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Diamond 5.46 - 6.4 eV

Related Topics:
Diamond - EV

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Band gap engineering is the process of controlling or altering the band gap of a material by controlling the composition of certain semiconductor alloys, such as GaAlAs, InGaAs, and InAlAs. It is also possible to construct layered materials with alternating compositions by techniques like molecular beam epitaxy. These methods are exploited in the design of heterojunction bipolar transistors (HBTs) and laser diodes.

Related Topics:
Molecular beam epitaxy - Heterojunction bipolar transistor - Laser diode

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The distinction between semiconductors and insulators is a matter of convention. One approach is to consider semiconductors a type of insulator with a low band gap. Insulators with a higher band gap, usually greater than 3 eV, are not considered semiconductors and generally do not exhibit semiconductive behaviour under practical conditions. Mobility also plays a role in determining a material's informal classification.

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Band gap decreases with increasing temperature, in a process related to thermal expansion. Special purpose temperature-sensor integrated circuits such as the DS1621 exploit this property to provide electronic temperature readings. Band gap also depends on pressure. Bandgaps can be either direct or indirect bandgaps, depending on the band structure.

Related Topics:
Thermal expansion - Integrated circuits - Direct - Indirect bandgap - Band structure

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