solid-state physics Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state physics studies how the l ...

, the valence band and conduction band are the bands closest to the

Fermi level The Fermi level of a solid-state body is the thermodynamic work required to add one electron to the body. It is a thermodynamic quantity usually denoted by ''µ'' or ''E''F for brevity. The Fermi level does not include the work required to remove ...

, and thus determine the

electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allow ...

of the solid. In

nonmetal In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite). The electrons in nonmetals behave differentl ...

s, the

valence Valence or valency may refer to: Science * Valence (chemistry), a measure of an element's combining power with other atoms * Degree (graph theory), also called the valency of a vertex in graph theory * Valency (linguistics), aspect of verbs rel ...

band is the highest range of electron energies in which electrons are normally present at

absolute zero Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibration ...

temperature, while the conduction band is the lowest range of vacant electronic states. On a graph of the electronic band structure of a material, the valence band is located below the Fermi level, while the conduction band is located above it. The distinction between the valence and conduction bands is meaningless in metals, because conduction occurs in one or more partially filled bands that take on the properties of both the valence and conduction bands.

Band gap

In semiconductors and insulators the two bands are separated by a band gap, while in semimetals the bands overlap. A band gap is an energy range in a solid where no electron states can exist due to the quantization of energy. Within the concept of bands, the energy gap between the valence band and the conduction band is the band gap. Electrical conductivity of non-metals is determined by the susceptibility of electrons to be excited from the valence band to the conduction band.

Electrical conductivity

''Semiconductor band structure''
''See electrical conduction and semiconductor for a more detailed description of band structure.''

In solids, the ability of electrons to act as

charge carrier In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used ...

s depends on the availability of vacant electronic states. This allows the electrons to increase their energy (i.e., accelerate) when an

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

is applied. Similarly, holes (empty states) in the almost filled valence band also allow for conductivity. As such, the

of a solid depends on its capability to flow electrons from the valence to the conduction band. Hence, in the case of a semimetal with an overlap region, the electrical conductivity is high. If there is a small band gap (E_g), then the flow of electrons from valence to conduction band is possible only if an external energy (thermal, etc.) is supplied; these groups with small E_g are called

semiconductors A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

. If the E_g is sufficiently high, then the flow of electrons from valence to conduction band becomes negligible under normal conditions; these groups are called insulators. There is some conductivity in semiconductors, however. This is due to thermal excitation—some of the electrons get enough energy to jump the band gap in one go. Once they are in the conduction band, they can conduct electricity, as can the hole they left behind in the valence band. The hole is an empty state that allows electrons in the valence band some degree of freedom.

Band edge shifts of semiconductor nanoparticles

The edge shifting of size-dependent conduction and/or valence band is a phenomenon being studied in the field of semiconductor nanocrystals. The radius limit of occurrence of the semiconductor nanocrystal is the effective Bohr radius of the nanocrystal. The conduction and/or valence band edges shift to higher energy levels under this radius limit due to discrete optical transitions when semiconductor nanocrystal is restricted by the exciton. As a result of this edge shifting, the size of the conduction and/or valence band is decreased. This size-dependent edge shifting of conduction and/or valence band can provide plenty of useful information regarding the size or concentration of the semiconductor nanoparticles or band structures.

References

Citations

General references

* * * {{cite web , last=Nave , first=Carl R. (Rod) , date=1999 , title=Band Theory for Solids , url=http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html , publisher=Hyperphysics , access-date=8 December 2021

External links

Direct Band Gap Energy Calculator
Electronic band structures