Name: energy bands in metals and insulators
Uploaded: 2024-07-08T13:20:08.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

High School

Physical Science

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

HS-PS2-6

Semiconductors

I materiali sono ampiamente classificati in tre tipi come metalli, isolanti e semiconduttori.
I metalli non hanno bande proibite di energia a causa della sovrapposizione delle bande di valenza e conduzione. Ciò consente il libero movimento degli elettroni, rendendo i metalli ottimi conduttori di elettricità.
Al contrario, gli isolanti hanno una grande banda proibita di energia, tipicamente maggiore di 3 eV. A temperatura ambiente, non si verifica alcuna conduzione perché l'energia termica o il campo elettrico applicato sono insufficienti per promuovere un numero significativo di elettroni dalla banda di valenza alla banda di conduzione, rendendoli cattivi conduttori.
I semiconduttori convenzionali come il silicio mostrano una banda proibita di energia stretta intorno a 1,1 eV. A temperatura ambiente, un numero significativo di elettroni può essere eccitato termicamente dalla banda di valenza alla banda di conduzione, provocando una piccola corrente.
Questa transizione genera vettori. Gli elettroni liberi agiscono come trasportatori nella banda di conduzione, mentre i vuoti creati dall'assenza di elettroni, noti come lacune, fungono da trasportatori nella banda di valenza.
I semiconduttori presentano una conduttività moderata, influenzata da fattori quali la temperatura, l'illuminazione della luce e le impurità droganti.

nozioni di base sui semiconduttori

Esiste una variazione nella conduttività elettrica dei materiali: metalli, semiconduttori e isolanti che vengono mostrati con l'aiuto dei diagrammi delle bande di energia.


Metalli come rame (Cu), zinco (Zn) o piombo (Pb) hanno una bassa resistività e presentano bande di conduzione che non sono completamente occupate o si sovrappongono alla banda di valenza, rendendo inesistente la banda proibita. Ciò consente agli elettroni nei livelli energetici più alti della banda di valenza, di passare facilmente alla banda di conduzione dopo aver ottenuto un'energia cinetica minima da un campo elettrico applicato. Di conseguenza, con molti stati disponibili vicini a quelli pieni, i metalli agevolano il facile flusso di corrente elettrica.


I semiconduttori hanno una banda di valenza piena e una banda di conduzione vuota, separate da un piccolo intervallo di banda, dell'ordine di 1 eV, che consente ad alcuni elettroni di valenza, di essere eccitati termicamente nella banda di conduzione a temperatura ambiente. Ciò si traduce in un numero moderato di portatori di carica, rendendo i semiconduttori più conduttivi degli isolanti ma meno dei metalli. L'energia di banda proibita varia per i semiconduttori, come 1,12 eV per il silicio (Si) e 1,42 eV per l'arseniuro di gallio (GaAs).


Negli isolanti come SiO2, la banda di valenza è piena di elettroni e la banda di conduzione è vuota. Gli isolanti hanno un ampio intervallo di banda, che rende difficile l'eccitazione degli elettroni di valenza dalla banda di conduzione a temperatura ambiente. Questo perché gli elettroni di valenza negli isolanti sono coinvolti in forti legami covalenti e richiedono una notevole energia per rompersi. Un ampio divario energetico separa le bande di valenza piena e quelle di conduzione vuote, e l'energia termica a temperatura ambiente è insufficiente per eccitare gli elettroni attraverso questo divario. Di conseguenza, sono disponibili pochissimi elettroni per la conduzione e il materiale non può condurre efficacemente la corrente elettrica.

Nozioni di Base sui Semiconduttori

I materiali sono ampiamente classificati in tre tipi come metalli, isolanti e semiconduttori.
I metalli non hanno bande proibite di energia a causa della sovrapposizione ...

Education

Didattica

JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

Basics of Semiconductors

Fondamenti dei semiconduttori

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 move into nearby states with very little added kinetic energy. That is why metals let electric current flow easily.

Semiconductors sit between metals and insulators. They have a filled valence band and an empty conduction band, separated by a small band gap of about 1 eV. At room temperature, some valence electrons can gain enough thermal energy to jump into the conduction band. This creates a moderate number of charge carriers, so semiconductors conduct better than insulators but not as well as metals. Silicon has a band gap of 1.12 eV, and gallium arsenide has a band gap of 1.42 eV.

Insulators such as SiO2 have a filled valence band and an empty conduction band, but the gap between them is large. Valence electrons are tied up in strong covalent bonds and need much more energy to move into the conduction band. Room-temperature thermal energy is not enough to bridge this gap. As a result, very few electrons can carry charge, and the material does not conduct electricity effectively.

Energy Bands in Metals and Insulators

energy bands in solids

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...

semiconductors

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

Compare metals, semiconductors, and insulators using energy band diagrams. Learn how band gaps, charge carriers, and resistivity affect electrical conductivity.

Energy Bands in Metals and Insulators | 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

Newton's Second Law

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Analyze data to support the claim that Newton's second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration. 

Clarification statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object sliding down a ramp, or a moving object being pulled by a constant force. 

Assessment Boundary: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.

HS-PS2-1

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HS-PS2-2

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Collisions in Multiple Dimensions: Problem Solving

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HS-PS2-3

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HS-PS2-4

Magnetic Fields

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Lenz's Law

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HS-PS2-5

Bonding in Metals

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Band Theory

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Conductors and Insulators

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Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. 

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Assessment Boundary: Assessment is limited to provided molecular structures of specific designed materials.

Energy Bands in Metals and Insulators

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