Band Theory - Revision history

Cpeterson70: Add to theory category

2025-01-27T22:49:33Z

Add to theory category

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	# Optical Properties: The absorption and emission of light in semiconductors are tied to transitions between valence and electron bands. For example: materials with large energy band gaps that are insulators (such as glass) appear transparent, since the minimum energy required for the photoelectric effect is great, and absorbed light is simply remitted.		# Optical Properties: The absorption and emission of light in semiconductors are tied to transitions between valence and electron bands. For example: materials with large energy band gaps that are insulators (such as glass) appear transparent, since the minimum energy required for the photoelectric effect is great, and absorbed light is simply remitted.

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			[[Category:Theory]]

Cpeterson70: Refine and add additional section

2025-01-27T22:45:52Z

Refine and add additional section

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	Band theory can help characterize different insulators, semi-conductors, and conductors. It provides a way to visualize how electrons behave in a material and why certain materials have specific electrical and thermal properties.		Band theory can help characterize different insulators, semi-conductors, and conductors. It provides a way to visualize how electrons behave in a material and why certain materials have specific electrical and thermal properties.

	== Principles ==		== Principles ==
	Electrons around an atom are organized into orbitals according to their discrete energy levels. These energy levels are quantized and orbitals are filled starting from the lowest. However, in solid materials, these energy levels overlap causing energy bands to form. ~~How far apart~~ and ~~how large~~ these bands ~~are~~ depend on the nature of the material and its atomic structure. Since there are infinite energy levels in an atom, there are an infinite number of bands. ~~Two certain~~ bands surrounding gap ~~between bands~~ are given names:		Electrons around an atom are organized into orbitals according to their discrete energy levels. These energy levels are quantized, and orbitals are filled starting from the lowest to the highest. However, in solid materials, these energy levels overlap causing energy bands to form. The spacing and size of these bands depend on the nature of the material and its atomic structure. Since there are effectively an infinite energy levels in an atom, there are an infinite number of potential bands. Among these, two important bands surrounding a band gap are given specific names:

			# Valence band: The valence band is the highest band that is fully occupied by electrons at 0 degrees kelvin. This band is composed of the valence orbitals of the atom.
			# Conduction band: The conduction band is the lowest unoccupied band above the valence band. Electrons in this band are free to move and contribute to electrical conductivity.

			The band gap is the separation of the bands. The properties of this gap determine whether a material behaves as an insulator, semi-conductor, or conductor.

			# Insulator: An insulator's band gap is relatively "large", and is typically greater than 4eV. The large gap prevents electrons from gaining enough energy to "jump" to the conduction band from the valence band, making the material a poor conductor.

			# Semi-conductor: A semi-conductor's band gap is "small", ranging from 0.1eV to 4eV. This gap allows electrons that gain sufficient energy (thermally or optically) to jump to the conduction band and allowing conductivity. Semi-conductors can be doped to shift the band gap up or down.

			# Conductors: Conductors have no significant band gap and electrons can freely move between the valence and conduction band.

			== Band Theory and Material Properties ==
			In addition to electrical conductivity, the behavior of electrons within bands also determines a material's properties such as its thermal conductivity and optical properties.

	# ~~Valence band~~: ~~The valence band is the closest band above the band gap. This band is composed of the valence orbitals of the atom.~~		# Thermal Conductivity: Free electrons within conductors contribute to heat transfer.
	~~# Conduction band: Conversely, the conduction is the closest band below the band gap~~.

	~~In insulators, the band gap~~ between ~~the~~ valence and ~~conduction~~ bands ~~is "~~large~~" and the bands do not overlap the Fermi level. In metals~~, the ~~Fermi level overlaps at least one band. However, in semi-conductors,~~ the ~~Fermi level~~ is ~~contained within a band gap. While band gaps in insulators may contain the Fermi level~~, ~~in semi-conductors, the gap between bands~~ is ~~"small"~~.		# Optical Properties: The absorption and emission of light in semiconductors are tied to transitions between valence and electron bands. For example: materials with large energy band gaps that are insulators (such as glass) appear transparent, since the minimum energy required for the photoelectric effect is great, and absorbed light is simply remitted.

Cpeterson70: Create Band Theory page

2025-01-09T21:17:07Z

Create Band Theory page

New page

[[File:Page-under-construction.png|400px|thumb|left]]

Band theory can help characterize different insulators, semi-conductors, and conductors. It provides a way to visualize how electrons behave in a material and why certain materials have specific electrical and thermal properties.

== Principles ==
Electrons around an atom are organized into orbitals according to their discrete energy levels. These energy levels are quantized and orbitals are filled starting from the lowest. However, in solid materials, these energy levels overlap causing energy bands to form. How far apart and how large these bands are depend on the nature of the material and its atomic structure. Since there are infinite energy levels in an atom, there are an infinite number of bands. Two certain bands surrounding gap between bands are given names:

# Valence band: The valence band is the closest band above the band gap. This band is composed of the valence orbitals of the atom.
# Conduction band: Conversely, the conduction is the closest band below the band gap.

In insulators, the band gap between the valence and conduction bands is "large" and the bands do not overlap the Fermi level. In metals, the Fermi level overlaps at least one band. However, in semi-conductors, the Fermi level is contained within a band gap. While band gaps in insulators may contain the Fermi level, in semi-conductors, the gap between bands is "small".