Name: valence and conduction bands in silicon
Uploaded: 2024-07-08T13:20:08.000Z
Duration: 1 min 1 s
Channel: JoVE

Los sólidos están compuestos por átomos con distintas configuraciones electrónicas y niveles de energía.
Cuando dos átomos aislados idénticos se acercan, su interacción hace que cada nivel de energía se divida en dos niveles distintos.
Esta división es el resultado del principio de exclusión de Pauli, que establece que no hay dos electrones en un átomo que puedan ocupar el mismo estado de energía al mismo tiempo.
Si varios átomos se juntan para formar un sólido, los niveles de energía se dividen para formar una banda continua. En el espaciado interatómico de equilibrio, la banda se divide en la banda de valencia y la banda de conducción.
A temperatura de cero absoluto, la banda de valencia comprende los niveles de energía llenos de electrones.
Por encima de la banda de valencia se encuentra la banda de conducción, que contiene los niveles de energía vacantes.
La brecha de energía entre estas dos bandas se denomina banda prohibida. Representa la diferencia de energía entre la parte superior de la banda de valencia y la parte inferior de la banda de conducción.

conceptos básicos de semiconductores

Energy Bands in Solids

Los átomos aislados tienen niveles de energía discretos que están bien descritos por el modelo de Bohr. Y cuantifica la energía de un electrón en un átomo de hidrógeno como E_n. Los números cuánticos 'n' más altos producen niveles de energía de electrones menos negativos y más cercanos.
Formación de banda:
Cuando los átomos se acercan, como en un sólido, estos niveles de energía discretos comienzan a dividirse debido a la superposición de los orbitales de los electrones de los átomos adyacentes. Esta división se produce debido al principio de exclusión de Pauli, que establece que dos electrones no pueden ocupar simultáneamente el mismo estado cuántico. A medida que se combinan más átomos, aumenta el número de niveles de energía discretos y la división se vuelve tan fina que forma una banda de energía continua. En un punto determinado, conocido como distancia interatómica de equilibrio, estas bandas se convierten en la banda de valencia, llena de electrones, y en la banda de conducción, que está vacía a temperatura del cero absoluto.
Bandas de energía en semiconductores:
La estructura de bandas de energía es más compleja en semiconductores como el silicio, que tiene 14 electrones. Los 10 electrones internos ocupan los niveles de energía más profundos y no contribuyen al enlace. Los cuatro electrones de valencia restantes, que se encuentran en las subcapas 3s y 3p, determinan las propiedades químicas y eléctricas del material. A medida que los átomos de silicio forman una red cristalina, las subcapas 3s y 3p se superponen y forman bandas. En la distancia de equilibrio en el cristal, estas bandas contienen 4N estados para la banda de valencia y 4N estados para la banda de conducción, donde N es el número de átomos de silicio.
El tamaño de la banda prohibida es crucial porque determina la facilidad con la que los electrones pueden excitarse en la banda de conducción. Esta banda prohibida es lo suficientemente pequeña para los semiconductores como para que la energía térmica o la luz puedan excitar electrones a través de la brecha, lo que resulta en una conducción eléctrica.

Conceptos básicos de semiconductores

Los sólidos están compuestos por átomos con distintas configuraciones electrónicas y niveles de energía.
Cuando dos átomos aislados idénticos se acercan, ...

Education

Educación

JoVE Core

Electrical Engineering

Ingeniería Eléctrica

Unit 1

Unidad 1

Basics of Semiconductors

Conceptos básicos de los semiconductores

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

valence and conduction bands in silicon

Valence and conduction bands explain how electrons behave in solids. In isolated atoms, electrons occupy discrete energy levels that the Bohr model describes well. The hydrogen atom, for example, has specific electron energies labeled by the quantum number n, and higher n values give levels that are less negative and closer together.

When atoms move close together in a solid, those discrete levels start to split. This happens because electron orbitals from neighboring atoms overlap. The Pauli exclusion principle also applies, since no two electrons can share the same quantum state. As more atoms are added, the splitting becomes so small that it appears as a continuous energy band.

At the equilibrium interatomic distance, these bands form the valence band and the conduction band. The valence band is filled with electrons at this point. The conduction band is empty at absolute zero temperature. This separation helps explain why some solids conduct electricity and others do not.

Silicon shows how band formation works in a semiconductor. A silicon atom has 14 electrons, but the inner 10 electrons stay in deep energy levels and do not take part in bonding. The remaining four valence electrons, which occupy the 3s and 3p subshells, control the material’s chemical and electrical behavior. As silicon atoms arrange into a crystal lattice, the 3s and 3p subshells overlap and form bands.

In the crystal, the valence band and conduction band each contain 4N states, where N is the number of silicon atoms. The bandgap, or energy gap between the bands, is important because it controls how easily electrons can move into the conduction band. In semiconductors, this gap is small enough that thermal energy or light can excite electrons across it, which allows electrical conduction.

Valence and Conduction Bands in Silicon

energy bands in solids

Valence and conduction bands explain how electrons behave in solids. In isolated atoms, electrons occupy discrete energy levels that the Bohr model describes well. The hydrogen atom, for example, has specific electron energies labeled by the quantum number n, and higher n values give levels that are less negative and closer together. When atoms move close together in a solid, those discrete levels start to split. This happens because electron orbitals from neighboring atoms overlap. The Pauli...

semiconductors

Energy Bands in Metals and Insulators

Materials conduct electricity in different ways because their energy bands are arranged differently. Metals, semiconductors, and insulators can be compared with energy band diagrams. These diagrams show how easily electrons can move when an electric field is applied. Metals such as copper, zinc, and lead have low resistivity. Their conduction band is not fully occupied, or it overlaps with the valence band, so a band gap is essentially absent. Electrons in the highest valence energy levels can...

types of semiconductors

Intrinsic and Doped Semiconductors

Intrinsic semiconductors are very pure materials with no impurities. At absolute zero, they act as perfect insulators because the valence electrons are bound and the conduction band is empty. That means electrical conduction cannot occur under those conditions. The Fermi level helps describe the chance that an energy level is occupied by an electron at thermal equilibrium. In an intrinsic semiconductor, the Fermi level sits near the middle of the band gap at absolute zero. As temperature...

carrier generation and recombination

Semiconductor Charge Carriers: Creation and Loss

Carrier generation and recombination control how free charge carriers change inside a semiconductor. Carrier generation creates electron-hole pairs, or EHPs, when electrons move from the valence band into the conduction band and leave holes behind. Carrier recombination does the opposite and lowers the number of free carriers. In direct-bandgap semiconductors such as gallium arsenide, generation happens efficiently because energy absorption can move a valence electron straight to the...

carrier transport

Drift and Diffusion in Semiconductors

Drift and diffusion are the two main ways electric current forms in semiconductors. These charge-carrier motions help determine how semiconductor devices work and how well they perform. The carriers involved are electrons and holes. Drift current begins when an external electric field acts on charge carriers. Electrons and holes move between collisions with lattice atoms, and this motion creates drift velocity. For electrons, drift velocity depends on electron mobility and the electric field...

p-n junction

P-N Junction Depletion Region

A p-n junction forms when p-type and n-type semiconductor materials are joined together. At the boundary, holes from the p-side and electrons from the n-side diffuse into the opposite side because of the concentration gradient. This movement leaves a region with no free charge carriers near the junction, called the depletion region. The charge density in the depletion region can be described on the n-side and p-side using the donor and acceptor doping concentrations, ND and NA. The fixed...

biasing of p-n junction

P-N Junction Diode Under Bias

P-N junction diodes change behavior under equilibrium, forward bias, and reverse bias. In equilibrium, no external voltage is applied across the junction. Carriers diffuse at the boundary and leave behind charged dopants. Acceptors remain on the p-side, and donors remain on the n-side. These fixed charges form a depletion region and an electric field that blocks further diffusion. The band diagram at equilibrium shows the Fermi levels on both sides aligned. That alignment means the junction is...

metal-semiconductor junctions

Schottky and Ohmic Metal Contacts

Metal contacts with semiconductors can form either Schottky or Ohmic junctions. The result depends on the work function of the metal, the work function of the semiconductor, and how electrons move when the two materials touch. At equilibrium, the Fermi levels align, so charge shifts until both sides match in energy. Schottky barriers form when a metal with work function Φm contacts a semiconductor with a different work function Φs. If Φm is greater than Φs, the semiconductor Fermi level starts...

biasing of metal-semiconductor junctions

How Bias Changes Metal-Semiconductor Current

Biasing metal-semiconductor junctions means applying a voltage across the junction. The metal connects to the voltage source, and the semiconductor is grounded. This setup helps control the direction and size of current in devices such as diodes, transistors, and photovoltaic cells. In a Schottky junction with an n-type semiconductor, a positive voltage on the metal lowers its Fermi level. A Fermi level is the energy level that helps describe how electrons are distributed. Lowering this level...

fermi level

Fermi Level in Semiconductors

The Fermi level is a key energy level in semiconductors. It sits between the lower-energy valence band and the higher-energy conduction band. The Fermi-Dirac function, which follows an S-shaped curve, shows the chance that an energy state is filled by an electron at a given temperature. At absolute zero, electrons occupy every energy state up to the Fermi level. States above it stay empty. As temperature rises, electrons gain energy and can move into vacant states above the Fermi level. In an...

fermi level dynamics

Vacuum Level and Schottky Barriers

Vacuum level and Schottky barriers help explain how electrons move between materials. The vacuum level is the energy needed for an electron to escape a material surface. In a semiconductor, it usually sits above the conduction band and serves as a reference for comparing electron energy. Electron affinity is the energy gap between the conduction band minimum and the vacuum level. It shows how easily a semiconductor can accept extra electrons. The work function is the least energy needed to...

key terms and concepts

Learn how atomic energy levels split into valence and conduction bands, and why silicon’s small bandgap lets heat or light drive conduction.

Valence and Conduction Bands in Silicon | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Valence and Conduction Bands in Silicon

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