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

Festkörper bestehen aus Atomen mit unterschiedlichen elektronischen Konfigurationen und Energieniveaus.
Wenn zwei identische isolierte Atome nahe zusammengebracht werden, führt ihre Wechselwirkung dazu, dass sich jedes Energieniveau in zwei unterschiedliche Niveaus aufspaltet.
Diese Aufspaltung ist eine Folge des Pauli-Ausschlussprinzips, das besagt, dass keine zwei Elektronen in einem Atom gleichzeitig den gleichen Energiezustand einnehmen können.
Werden mehrere Atome zu einem Festkörper zusammengeführt, spalten sich die Energieniveaus zu einem kontinuierlichen Band auf. Im interatomaren Gleichgewichtsabstand spaltet sich das Band in das Valenzband und das Leitungsband.
Bei Temperaturen zum absoluten Nullpunkt umfasst das Valenzband die Energieniveaus, die mit Elektronen gefüllt sind.
Oberhalb des Valenzbandes liegt das Leitungsband, das freie Energieniveaus enthält.
Die Energielücke zwischen diesen beiden Bändern wird als Bandlücke bezeichnet. Sie stellt die Energiedifferenz zwischen der Oberseite des Valenzbandes und der Unterseite des Leitungsbandes dar.

grundlagen der halbleitertechnik

Energy Bands in Solids

Isolierte Atome haben diskrete Energieniveaus, die durch das Bohr-Modell gut beschrieben werden. Und es quantifiziert die Energie eines Elektrons in einem Wasserstoffatom als E_n. Höhere Quantenzahlen „n“ ergeben weniger negative, näher beieinander liegende Elektronenenergieniveaus.

Bandbildung:

Wenn Atome einander nahe gebracht werden, wie in einem Festkörper, beginnen sich diese diskreten Energieniveaus aufgrund der Überlappung der Elektronenorbitale benachbarter Atome aufzuspalten. Diese Aufspaltung erfolgt aufgrund des Pauli-Prinzips, das besagt, dass keine zwei Elektronen gleichzeitig denselben Quantenzustand einnehmen können. Wenn mehr Atome kombiniert werden, erhöht sich die Anzahl der diskreten Energieniveaus und die Aufspaltung wird so fein, dass sie ein kontinuierliches Energieband bildet. An einem bestimmten Punkt, der als Gleichgewichtsabstand zwischen den Atomen bezeichnet wird, werden diese Bänder zum Valenzband, das mit Elektronen gefüllt ist, und zum Leitungsband, das bei der absoluten Nulltemperatur leer ist.

Energiebänder in Halbleitern:

Die Energiebandstruktur ist in Halbleitern wie Silizium, das 14 Elektronen hat, komplexer. Die inneren 10 Elektronen besetzen die tiefer liegenden Energieniveaus und tragen nicht zur Bindung bei. Die verbleibenden vier Valenzelektronen, die sich in den 3s- und 3p-Unterschalen befinden, bestimmen die chemischen und elektrischen Eigenschaften des Materials. Wenn Siliziumatome ein Kristallgitter bilden, überlappen sich die 3s- und 3p-Unterschalen und bilden Bänder. Beim Gleichgewichtsabstand im Kristall enthalten diese Bänder 4N Zustände für das Valenzband und 4N Zustände für das Leitungsband, wobei N die Anzahl der Siliziumatome ist.

Die Bandlückengröße ist entscheidend, da sie bestimmt, wie leicht Elektronen in das Leitungsband angeregt werden können. Diese Bandlücke ist für Halbleiter klein genug, dass thermische Energie oder Licht Elektronen über die Lücke hinweg anregen können, was zu elektrischer Leitung führt.

Grundlagen der Halbleitertechnik

Festkörper bestehen aus Atomen mit unterschiedlichen elektronischen Konfigurationen und Energieniveaus.
Wenn zwei identische isolierte Atome nahe zusammengebracht werden, ...

Education

Lehre

JoVE Core

Electrical Engineering

Elektrotechnik

Unit 1

Einheit 1

Basics of Semiconductors

Grundlagen der Halbleiter

KEY TERMS AND CONCEPTS

ZENTRALE BEGRIFFE UND KONZEPTE

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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