Are you an EPFL student looking for a semester project?
Work with us on data science and visualisation projects, and deploy your project as an app on top of GraphSearch.
Concept
Valence and conduction bands
Summary
In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states. On a graph of the electronic band structure of a semiconducting 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 conductors 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.
Semiconductor band structureSee electrical conduction and semiconductor for a more detailed description of band structure.
In solids, the ability of electrons to act as charge carriers depends on the availability of vacant electronic states. This allows the electrons to increase their energy (i.e., accelerate) when an electric field is applied. Similarly, holes (empty states) in the almost filled valence band also allow for conductivity.
As such, the electrical conductivity 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 (Eg), then the flow of electrons from valence to conduction band is possible only if an external energy (thermal, etc.
Official source
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related people (106)
Related concepts (16)
Electronic band structure
In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called band gaps or forbidden bands). Band theory derives these bands and band gaps by examining the allowed quantum mechanical wave functions for an electron in a large, periodic lattice of atoms or molecules.
Solid-state physics
Solid-state physics is the study of rigid matter, or solids, through methods such as solid-state chemistry, quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state physics studies how the large-scale properties of solid materials result from their atomic-scale properties. Thus, solid-state physics forms a theoretical basis of materials science. Along with solid-state chemistry, it also has direct applications in the technology of transistors and semiconductors.
Electron hole
In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle denoting the lack of an electron at a position where one could exist in an atom or atomic lattice. Since in a normal atom or crystal lattice the negative charge of the electrons is balanced by the positive charge of the atomic nuclei, the absence of an electron leaves a net positive charge at the hole's location. Holes in a metal or semiconductor crystal lattice can move through the lattice as electrons can, and act similarly to positively-charged particles.
Related courses (32)
EE-567: Semiconductor devices II
Students will learn about understanding the fundamentals and applications of emerging nanoscale devices, materials and concepts.
Remark: at least 5 students should be enrolled for the course to be g
PHYS-310: Solid state physics II
Ce cours de deux semestres donne une introduction à la Physique du solide, à la structure cristalline, aux vibrations du réseau, aux propriétés électroniques, de transport thermique et électrique ains
MSE-484: Properties of semiconductors and related nanostructures
This course explains the origin of optical and electrical properties of semiconductors. The course elaborates how they change when the semiconductors are reduced to sizes of few nanometers. The course
Related MOOCs (4)
Electronics
Introduction à l’électronique analogique- seconde partie. Fonctions linéaires de base réalisée à l’aide de transistor bipolaire.
Electronics
Introduction à l’électronique analogique- seconde partie. Fonctions linéaires de base réalisée à l’aide de transistor bipolaire.
Synchrotrons and X-Ray Free Electron Lasers (part 1)
Synchrotrons and X-Ray Free Electron Lasers (part 1)