Image source: google
Hello friends of steemit one way to study semiconductors is through optical properties but before we have to know some basic concepts.
What are photons?
A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual photons).
More details here the link: photons
Image source: google
What is a phonon?
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids. Often designated a quasiparticle
More details here the link: phonon
Image source: google
Valence band and conduction band
In solid-state physics, the valence band and conduction band are the closest to the Fermi level and thus determine the electrical conductivity of the solid.
Valence band
In solids theory, the band of valence is called the highest of the ranges of electron energies (or bands) that is occupied by electrons in absolute zero.
conduction band
Is the range of electronic energies that, being above the valence band, allows the electrons to undergo accelerations by the presence of an external electric field and, therefore, allows the presence of electric currents.
Band prohibited
The forbidden band of a semiconductor is the minimum energy required to excite an electron from its connected state to a free state that allows it to participate in conduction.
More details here the link: [1] [2]
Direct transitions and indirect transitions
There are two types of transitions, in which only the photon yields energy and those in which the crystal lattice transfers energy and therefore one or more phonons are emitted or absorbed simultaneously with the absorption of the photon.
Direct transitions: these take place when the wave vector of the maximum of the valence band and the minimum of the conduction band coincide and consequently the moment is conserved.
Indirect transitions: occurs when the ǩ wave vectors of the maximum of the band of the valence band and the minimum of the conduction band do not coincide, so a change of both energy and momentum is required.
Since the photon alone can not cause the change of momentum, the momentum is conserved by the process of absorption or emission of a phonon.
More details here the link: [3]
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Nice post! :) I like to think of phonons as lattice vibrations.
I think Bloch's Theorem is a really neat result. It's potentially my favourite theorem in condensed matter physics. The quick take-away from it is that electron transport through the lattice comes with no associated energy cost. Fun to imagine creation/annihilation of electrons at various lattice sites.
Great post! Refreshing some knowledge :)