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".
An intrinsic 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 , the probability of these excitations occurring is proportional to:
Encyclopedia
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".
An intrinsic 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 , the probability of these excitations occurring is proportional to:
where:
- e is the exponential function
- Eg is the band gap energy
- k is Boltzmann's constant
...
- T is temperature
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.
Band gaps |
| Common materials at room temperature |
|
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 ,
laser diodes and
solar cells.
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.
Band gap decreases with increasing temperature, in a process related to thermal expansion. Special purpose
integrated circuits such as the DS1621 exploit this property to perform accurate temperature measurements. Band gap also depends on pressure. Bandgaps can be either direct or
indirect bandgaps, depending on the
band structure.
See also
Chemicals
Germanium is a chemical element [i] in the periodic table [i] that has the symbol
Ge and atomic number [i] ...
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