exciton, the combination of an electron and a positive hole (an empty electron state in a valence band), which is free to move through a nonmetallic crystal as a unit. Fast Facts.
What is exciton and its types?
This is termed as exciton. In organic materials two models are used: the band or wave model (low temperature, high crystalline order) and the hopping model (higher temperature, low crystalline order or amorphous state). Energy transfer in the hopping limit is identical with energy migration.
Is an exciton a real particle?
It actually sounds like a subatomic particle, but it is a little more complicated than that. An exciton is a bound state of an electron and an electron hole and is technically a boson. You are probably familiar with the idea of an electron hole from semiconductor physics.
What is exciton in semiconductor?
Excitons are quasi-particles that form when Coulomb-interacting electrons and holes in semiconductors are bound into pair states. They have many features analogous to those of atomic hydrogen. … Excitonic signatures commonly appear in the optical absorption and emission of direct-gap semiconductor systems.
What is the meaning of exciton?
An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and some liquids.
What is exciton binding energy?
Exciton binding energy is the measure of the coulombic attraction between electron and hole wavefunction.
What is exciton recombination?
As a result of absorption of photons of energy equal or greater than the band gap energy of the semiconductor, the excitons (electrons and holes) are generated in the conduction and valence band, respectively. … This is called exciton recombination. The same phenomenon is also present in an organic semiconductor.
What is free exciton?
A free exciton is a bound electron-hole pair that has a binding energy of a few meV. Generation of electron-hole pairs in a semiconductor can be achieved by illuminating a semiconductor sample with light with photon energies larger than the energy gap of the semiconducto.
What is self trapped exciton?
Self-trapped excitons (STEs), occurring in a material with soft lattice and strong electronphonon coupling, emit photons with broad spectrum and large Stokes shift. Recently, series halide perovskites with efficient STE emission have been reported and showed promise for solid-state lighting.
Is photon a quasiparticle?
In materials, a photon quasiparticle is a photon as affected by its interactions with the material. … A polaron is a quasiparticle which comes about when an electron interacts with the polarization of its surrounding ions. An exciton is an electron and hole bound together.
Which is a semiconductor?
Semiconductors are substances with properties somewhere between them. ICs(integrated circuits) and electronic discrete components such as diodes and transistors are made of semiconductors. Common elemental semiconductors are silicon and germanium. Silicon is well-known of these. Silicon forms most of ICs.
Are excitons bosons?
Bosons comprising this gas are mixtures of separate excitons, and the non-bosonic nature of excitons leads only to a renormalization of the interaction between them. Features of the exciton luminescence coming from the interaction and non-bosonic nature of excitons are considered.
Where can I find exciton binding energy?
Abstract: For small organic conjugated molecules the exciton binding energy can be calculated treating molecules as conductor, and is given by a simple relation BE e2/(40R), where is the dielectric constant and R is the equivalent radius of the molecule.
What is exciton radius?
Exciton Bohr radius can be defined as the separation distance between electron and hole. We all know that the charge carriers can move freely in bulk semiconductor, thus the wavefunction looks much like a hydrogen atom. … The distance between the electron hole pair is exciton Bohra radius.
What is excitonic effect?
When nanostructure sizes become smaller than the bulk exciton Bohr radius, excitonic effects are significantly enhanced with reducing size or dimensionality. … These excitonic effects originate from electron-hole Coulombic interactions, which strongly enhance the oscillator strength between the electron and hole.
What is Bohr exciton?
An exciton bohr radius is the distance in an electron-hole pair. A Quantum Dot is a semiconductor so small that the size of the crystal is on the same order as the size of the exciton bohr radius. This unique size property causes the band of energies to turn into discrete energy levels.
What is positive hole?
A positive hole in a semiconductor is a vacancy which is created at the site of a covalent bond when an electron leaves a covalent bond.
What is excitonic coupling?
Abstract. When two or more identical chromophores are placed in close proximity, the excited states of chromophores interact with each other, and the excited state can delocalize over all chromophores as an exciton. This interaction is called ‘Exciton Coupling.
What is exciton binding energy of ZnO?
Zinc oxide (ZnO) is an extremely versatile n-type semiconductor material with a large exciton binding energy of 60 meV and a large band-gap energy of 3.37 eV at room temperature (259,260).
How is exciton energy calculated?
In GaAs, the 3D bulk exciton binding energy is equal to -4.8 meV with a Bohr radius of =11.6 nm. In CdTe it is equal to -10.0 meV with a Bohr radius of =6.8 nm. Thus the energy of the exciton, i.e. the band gap transition, reads: GaAs: Eex=Egap+Eex,b=1.519 eV0.005 eV=1.514 eV.
Does exciton take part in electrical conduction?
Since the excitation is electrically neutral, the exciton lines do not contribute directly to electrical conduction.
What is excitonic resonance?
The excitonic states are computed taking into account both the renormalization of the electronhole interaction and self-energy effects induced by the metallic segment on the electronhole pair, as well as by the dielectric environment, through an induced charge numerical approach.
What is electron hole pair?
The electronhole pair is the fundamental unit of generation and recombination in inorganic semiconductors, corresponding to an electron transitioning between the valence band and the conduction band where generation of electron is a transition from the valence band to the conduction band and recombination leads to a …
What is the difference between optical band gap and electronic band gap?
Electrical band gap is the minimal energy required to create an electron hole pair in a semiconductor, whereas optical band gap is the exciton energy which determines the onset of vertical interband transitions. … Electronic band gap is the term used for the gap between the valence band maxima and conduction band minima.
What is Auger recombination?
Auger recombination is a non-radiative process involving three carriers. Direct Auger recombination occurs when an electron and hole recombine, but instead of producing light, either an electron is raised higher into the conduction band or a hole is pushed deeper into the valence band, as shown in Fig.
What does self trapped mean?
When an electron or a hole is inserted into an insulator, it often gets self-trapped by deforming the local lattice structure. This permits a localized bound state to form with a lower energy than simple insertion of an electron or hole into the conduction or valence band.
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