Indirect bandgap - Wikipedia, the free encyclopedia
Semiconductors that have an indirect bandgap are inefficient at emitting light. ... Silicon is an indirect bandgap semiconductor, and hence is not generally useful ...
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Direct bandgap - Wikipedia, the free encyclopedia
In indirect bandgap semiconductors such as crystalline silicon, ... light emission from indirect semiconductors is very inefficient ... indirect bandgap for ...
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Indirect Bandgap Semiconductors
... light emitting devices, indirect band gap semiconductors are not at all promising. To see why, consider the band edge diagram of an indirect band gap semiconductor. ...
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Britney Spears Guide to Semiconductor Physics: Indirect-gap semiconductors.
Britney Spears discusses the basic concepts behind ... Indirect Bandgap ... For light emitting devices, indirect band gap semiconductors are not at all ...
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Indirect-to-direct band gap transitions in phosphorus adsorbed ?112? ...
Using first-principles calculations, we investigated the modification of the band structures of silicon nanowires (SiNWs) that were adsorbed with phosphorus atoms. ...
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Energy Citations Database (ECD) - - Document #779728
We investigate the quantum size effects of the pressure-induced direct-to-indirect band gap transition in InP nanocrystals. Hydrostatic pressures of up to 13 GPa ...
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Strain dependence of indirect band gap for strained silicon on ...
We have used low temperature photoluminescence measurements in order to quantify the impact of strain effect on the Si indirect band gap in 9 nm thick tensely ...
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Band Gap Engineering
Characteristics Direct and Indirect Bandgap Types (Click to see full size pictures) ... See also Direct Bandgap AlGaAs. Silicon. See also Indirect Bandgap AlGaAs ...
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Optoelectronic devices
Indirect bandgap semiconductors, i.e. semiconductors for which the minimum of ... For an indirect bandgap semiconductor, the conduction band is not vertically ...
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Off-zone-center or indirect band-gap-like hole transport in ...
Off-zone-center or indirect band-gap-like hole transport in heterostructures. Gerhard Klimeck, ... indirect-band-gap material, and 2 to capture this physics ...
hpc.jpl.nasa.gov

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In semiconductor physics, an indirect bandgap is a bandgap in which the minimum energy in the conduction band is shifted by a k-vector relative to the valence band. The k-vector difference represents a difference in momentum.

Semiconductors that have an indirect bandgap are inefficient at emitting light. This is because any electrons present in the conduction band quickly settle into the energy minimum of that band. Electrons in this minimum require some source of momentum allowing them to overcome the offset and fall into the valence band. Photons have very little momentum compared to this energy offset –. The momentum "kick" of a photon being emitted or absorbed is negligible and direct transitions are essentially 'vertical' in k-space.

Since the electron cannot rejoin the valence band by radiative recombination, conduction band electrons typically last quite some time before recombining through less efficient means. Silicon is an indirect bandgap semiconductor, and hence is not generally useful for light-emitting diodes or laser diodes.

However, the indirect (non-radiative) recombination takes place at point defects or at grain boundaries (surface) in Si. If the excited electrons are prevented from reaching these recombination places, they have no choice but to fall back into the valence band by radiative recombination. This can be done by creating a dislocation loop in the Silicon. At the edge of the loop, the planes above and beneath the "dislocation disk" are pulled apart, creating a negative pressure, which raises the energy of the conduction band substantially, with the result that the electrons cannot pass this edge. Provided that the area directly above the dislocation loop is defect-free (no non-radiative recombination possible), the electrons will fall back into the valence shell by radiative recombination and thus emitting light. This is the principle on which "DELEDs" (Dislocation Engineered LEDs) are based.

Likewise the absorption of light at an indirect gap is much weaker than at a direct one. As in the emission process both the laws of conservation of energy and of momentum must be observed, the only way to promote an electron from the top of the valence band to the bottom of the conduction band is to simultaneously emit (or absorb) a phonon that compensates for the missing momentum vector. However, such a combined transition has a much lower probability. This means, for example, that silicon is at a disadvantage as a potential solar material compared to a direct gap material like CuInSe2.

The absorption (read: color) of an indirect bandgap material usually depends more on temperature than that of a direct material, because at low temperatures (e.g. 4K) phonons are not available for a combined (vibronic) process. Silicon e.g. starts to transmit red light at these temperatures, because red photons do not have sufficient energy for a direct process.

In some materials with an indirect gap the value of the gap is negative, i.e. the top of the valence band is higher than the bottom of the conduction band in energy. Such materials are known as semimetals.

External links

• B. Van Zeghbroeck's Principles of Semiconductor Devices at Electrical and Computer Engineering Department of University of Colorado at Boulder
• Tongue in cheek, but accurate guide to Semiconductor physics ("Britney Spears")

Indirect bandgap - Wikipedia, the free encyclopedia
In semiconductor physics, an indirect bandgap is a bandgap in which the minimum energy in the conduction band is shifted by a k-vector relative to the valence band.

Image:Indirect Bandgap.svg - Wikipedia, the free encyclopedia
Indirect_Bandgap.svg ‎ (SVG file, nominally 600 × 480 pixels, file size: 6 KB) edit] Description. An image illustrating an indirect band gap in the E-k space between the valence ...

Britney Spears Guide to Semiconductor Physics: Indirect-gap ...
Indirect Bandgap Semiconductors. Not all semiconductor materials have the minimum of the conduction band above the ...

INEX: Wikipedia, the free encyclopedia (Indirect bandgap)
In semiconductor physics , an indirect bandgap is a bandgap in which the minimum energy in the conduction band is shifted by a k - vector , which is determined by the ...

Brown Technology Partnerships: Indirect-Bandgap Semiconductor Laser ...
Indirect-Bandgap Semiconductor Laser and Method to Fabricate Same. Inventor(s): Jimmy Xu Sylvain Cloutier. Summary This invention relates broadly to solid state optical emitter ...

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Indirect Bandgap-Like Current Flow inDirect Bandgap Electron Resonant ...
Indirect Bandgap-Like Current Flow inDirect Bandgap Electron Resonant Tunneling Diodes Gerhard Klimec k1 Þ Jet Propulsion Laboratory, California Institute of Technology, Pasadena ...

indirect addressing definition of indirect addressing in the Free ...
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calorimetry (kăl'ərĭm`ətrē), measurement of heat heat, nonmechanical energy in ... Indirect bandgap Indirect Battlefield Engagement System indirect bilirubin