For those unfamiliar with this, when a semiconductor has a direct band gap that means that it is likely to be suitable for devices that emit or detect photons, because when photons are absorbed, they generate electron-hole pairs, and when electron-hole pairs combine, their energy is released as photons.
In semiconductors with indirect band gap, when electron-hole pairs combine they usually just heat the material, instead of emitting light, which is why silicon, for instance, is not suitable for making LEDs.
While a direct band gap is desirable in LEDs, lasers and photodetectors, an indirect band gap is preferable in other applications where you do not want electrons and holes to recombine easily, e.g. in bipolar transistors or SCRs and in many kinds of diodes.
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For those unfamiliar with this, when a semiconductor has a direct band gap that means that it is likely to be suitable for devices that emit or detect photons, because when photons are absorbed, they generate electron-hole pairs, and when electron-hole pairs combine, their energy is released as photons.
In semiconductors with indirect band gap, when electron-hole pairs combine they usually just heat the material, instead of emitting light, which is why silicon, for instance, is not suitable for making LEDs.
While a direct band gap is desirable in LEDs, lasers and photodetectors, an indirect band gap is preferable in other applications where you do not want electrons and holes to recombine easily, e.g. in bipolar transistors or SCRs and in many kinds of diodes.