2/2/2024 0 Comments Indirection bandThe involvement of the phonon makes this process much less likely to occur in a given span of time, which is why radiative recombination is far slower in indirect band gap materials than direct band gap ones. It can also, instead, involve a crystallographic defect, which performs essentially the same role. For radiative recombination to occur in an indirect band gap material, the process must also involve the absorption or emission of a phonon, where the phonon momentum equals the difference between the electron and hole momentum. This is possible in a direct band gap semiconductor if the electron has a k-vector near the conduction band minimum (the hole will share the same k-vector), but not possible in an indirect band gap semiconductor, as photons cannot carry crystal momentum, and thus conservation of crystal momentum would be violated. One important process is called radiative recombination, where an electron in the conduction band annihilates a hole in the valence band, releasing the excess energy as a photon. A photon with an energy near a semiconductor band gap has almost zero momentum. Interactions among electrons, holes, phonons, photons, and other particles are required to satisfy conservation of energy and crystal momentum (i.e., conservation of total k-vector). Some III-V materials are indirect bandgap as well, for example AlSb. Indirect bandgap materials include crystalline silicon and Ge. In an "indirect" gap, a photon cannot be emitted because the electron must pass through an intermediate state and transfer momentum to the crystal lattice.Įxamples of direct bandgap materials include amorphous silicon and some III-V materials such as InAs and GaAs. The band gap is called "direct" if the crystal momentum of electrons and holes is the same in both the conduction band and the valence band an electron can directly emit a photon. If the k-vectors are different, the material has an "indirect gap". The minimal-energy state in the conduction band and the maximal-energy state in the valence band are each characterized by a certain crystal momentum (k-vector) in the Brillouin zone. In semiconductor physics, the band gap of a semiconductor can be of two basic types, a direct band gap or an indirect band gap. Types of energy range in a solid where no electron states can exist
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