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Encyclopedia > Electron hole

For the following two reasons the electron hole was introduced into calculations: If an electron is excited into higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconductors). In crystals band structure calculations lead to an effective mass for the charge carriers, which can be negative. Inspired by the Hall effect, Newtons law is used to slap the negative sign onto the charge. Auger electron spectroscopy is an analytical technique in surface chemistry and materials science. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... Computational chemistry is a branch of chemistry that uses the results of theoretical chemistry incorporated into efficient computer programs to calculate the structures and properties of molecules and solids, applying these programs to real chemical problems. ... Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily loses electrons to form positive ions (cations) and has metallic bonds between metal atoms. ... A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. ... In solid state physics, the electronic band structure, or simply band structure, refers to the dispersion relation (the relation between energy versus momentum) of electrons in a crystal. ... Hall effect diagram, showing electron flow (rather than conventional current). ... In the article vector quantities are written in bold whereas scalar ones are in italics. ...


Solid state physics

In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. A full (or nearly full) valence band is present in semiconductors and insulators. The concept of a hole is essentially a simple way to analyze the electronic transitions within the valence band. Solid-state physics, the largest branch of condensed matter physics, is the study of rigid matter, or solids. ... e- redirects here. ... In solids, the valence band is the highest range of electron energies where electrons are normally present at zero temperature. ... A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. ... This article or section is in need of attention from an expert on the subject. ...


Hole conduction can be explained by the following analogy. Imagine a row of people seated in an auditorium, where there are no spare chairs. Someone in the middle of the row wants to leave, so he jumps over the back of the seat into an empty row, and walks out. The empty row is analogous to the conduction band, and the person walking out is analogous to a free electron. In semiconductors and insulators, the conduction band is the range of electron energy, higher than that of the valence band, sufficient to make the electrons free to accelerate under the influence of an applied electric field and thus constitute an electric current. ...


Now imagine someone else comes along and wants to sit down. The empty row has a poor view; so he does not want to sit there. Instead, a person in the crowded row moves into the empty seat the first person left behind. The empty seat moves one spot closer to the edge and the person waiting to sit down. The next person follows, and the next, et cetera. One could say that the empty seat moves towards the edge of the row. Once the empty seat reaches the edge, the new person can sit down.


In the process everyone in the row has moved along. If those people were negatively charged (like electrons), this movement would constitute conduction. If the seats themselves were positively charged, then only the vacant seat would be positive. This is a very simple model of how hole conduction works. Electrical conductivity or specific conductivity is a measure of a materials ability to conduct an electric current. ...


In reality, due to the crystal structure properties, the hole is actually not localized to a single position as described in the previous example. Rather, the hole is delocalized and spans an area in the crystal lattice covering many hundreds of unit cells. This is equivalent to the idea that we cannot tell which broken bond corresponds to the 'missing' electron, and is supported by uncertainty theorems from quantum mechanics. Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Fig. ...


Instead of analysing the movement of an empty state in the valence band as the movement of billions of separate electrons, physicists propose a single imaginary particle called a "hole". In an applied electric field, all the electrons move one way, so the hole moves the other way. If a hole associates itself with a neutral atom, that atom loses an electron and becomes positive. The physicists therefore say that the hole must have positive charge—in fact, they assign a charge of +e—precisely the opposite of the electron charge. It has been suggested that optical field be merged into this article or section. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ...


Using Coulomb's law, we can calculate the force on the "hole" due to an electric field. Physicists then propose an effective mass which will relate the (imaginary) force on the (imaginary) hole to the acceleration of that hole. In some semiconductors (such as silicon), effective mass is dependent on direction (anisotropic), however a value averaged over all directions can be used for some macroscopic calculations. Coulombs torsion balance In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. ... In solid state physics, a particles effective mass is the mass it seems to carry in the semiclassical model of transport in a crystal. ... Look up anisotropy in Wiktionary, the free dictionary. ...


Holes in quantum chemistry

An alternate meaning for the term electron hole is used in computational chemistry. In coupled cluster methods, the ground (or lowest energy) state of a molecule is interpreted as the "vacuum state"—conceptually, in this state there are no electrons. In this scheme, the absence of an electron from a normally-filled state is called a "hole" and is treated as a particle, and the presence of an electron in a normally-empty state is simply called an "electron". This terminology is almost identical to that used in solid-state physics. Computational chemistry is a branch of chemistry that uses the results of theoretical chemistry incorporated into efficient computer programs to calculate the structures and properties of molecules and solids, applying these programs to real chemical problems. ... This article needs to be cleaned up to conform to a higher standard of quality. ...


See also


  Results from FactBites:
 
Electron hole - Wikipedia, the free encyclopedia (532 words)
In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band.
The physicists therefore say that the hole must have positive charge—in fact, they assign a charge of +e—precisely the opposite of the electron charge.
In this scheme, the absence of an electron from a normally-filled state is called a "hole" and is treated as a particle, and the presence of an electron in a normally-empty state is simply called an "electron".
Kids.net.au - Encyclopedia Semiconductor - (1272 words)
Semiconductors are useful for electronic purposes because they can carry an electric current by electron propagation or hole propagation, and because this current is generally uni-directional and the amount of current may be influenced by an external agent (see diode, transistor, amplifier etc.).
Electron propagation is the same sort of current flow seen in a standard copper wire - heavily ionized atoms pass excess electrons down the wire from one atom to another in order to move from a more negatively ionized area to a less negatively ionized area.
"Hole" propagation is a rather different proposition - in the case of a semiconductor experiencing hole propagation, the charge moves from a more positively ionized area to a less positively ionized area by the movement of the electron hole created by the absence of an electron in a nearly-full electron shell.
  More results at FactBites »

 
 

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