http://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps
http://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps
In the band structure of a semiconductor material, bandgap is the forbidden region between the valence band (VB) and the conduction band (CB) that cannot occupy by the electrons. In a direct bandgap semiconductor, the electrons in the minimum of the CB and the maximum of the VB have the same wave vectors and consequently electron transition only need to the energy conversation. However, there is a difference in the momentum of electrons in the minimum of CB and the maximum of the VB in an indirect ban gap semiconductor that limits the electron energy transition from VB to CB to the presence of a phonon for momentum conservation .
if min of CB and max VB be Exactly opposite , this is direct band gap and otherwise is in-direct band gap . some materials that is direct can generate light. for example GaAs.
Bandgap represents the minimum energy difference between the top of the valence band and bottom of the conduction band.
In a direct band gap semiconductor, the top of the valence band and the bottom of the conduction band occur at the same value of momentum. (A schematic representation of this statement may help you. You can visit -http://www.doitpoms.ac.uk/tlplib/semiconductors/direct.php - for the scheme.)
In an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum in the conduction band energy. (Again follow the above link for appropriate schematic representation.)
A photon of energy equal to the energy difference of VB and CB can produce an electron- hole pair in a direct band gap semiconductor very easily as the momentum of the VB and CB are same. But, in an indirect semiconductor, an electron having energy equal to the energy gap must acquire sufficient momentum to produce an electron- hole pair. This gain or loss of momentum depends on phonons, which is actually lattice vibrations.
Since, only photon is enough to produce an electron- hole pair in direct band gap semiconductors, it is much faster than the indirect band gap semiconductors in terms of the formation of the e- hole pair.
Bandgap represents the minimum energy difference between the top of the valence band and bottom of the conduction band.
In a direct band gap semiconductor, the top of the valence band and the bottom of the conduction band occur at the same value of momentum. (A schematic representation of this statement may help you. You can visit -http://www.doitpoms.ac.uk/tlplib/semiconductors/direct.php - for the scheme.)
In an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum in the conduction band energy. (Again follow the above link for appropriate schematic representation.)
A photon of energy equal to the energy difference of VB and CB can produce an electron- hole pair in a direct band gap semiconductor very easily as the momentum of the VB and CB are same. But, in an indirect semiconductor, an electron having energy equal to the energy gap must acquire sufficient momentum to produce an electron- hole pair. This gain or loss of momentum depends on phonons, which is actually lattice vibrations.
Since, only photon is enough to produce an electron- hole pair in direct band gap semiconductors, it is much faster than the indirect band gap semiconductors in terms of the formation of the e- hole pair.
Bro just simply to say that in direct band gap valence band lower & conduction band higher portion same level so minimum energy is needed for electron to shift up-wards while exactly opposite is the case with in-direct band gap
What is this E-K reciprocal space ? Can u elaborate your answer @ Driss Soubane
Http://www.acsu.buffalo.edu/~wie/applet/students/mcg/ternary.html
e-k diagram is an energy band diagram with detailed description
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Semiconductor