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

Materiały są ogólnie podzielone na trzy typy: metale, izolatory i półprzewodniki.
Metale nie mają przerwy energetycznej ze względu na nakładanie się pasm walencyjnych i przewodzących. Pozwala to na swobodny ruch elektronów, dzięki czemu metale są doskonałymi przewodnikami elektryczności.
W przeciwieństwie do tego, izolatory mają dużą przerwę energetyczną, zwykle większą niż 3 eV. W temperaturze otoczenia nie zachodzi przewodzenie, ponieważ energia cieplna lub przyłożone pole elektryczne są niewystarczające do przeniesienia znacznej liczby elektronów z pasma walencyjnego do pasma przewodnictwa, co czyni je słabymi przewodnikami.
Konwencjonalne półprzewodniki, takie jak krzem, wykazują wąską przerwę energetyczną około 1,1 eV. W temperaturze otoczenia znaczna liczba elektronów może być wzbudzona termicznie z pasma walencyjnego do pasma przewodnictwa, co skutkuje niewielkim prądem.
To przejście generuje przewoźników. Wolne elektrony działają jako nośniki w paśmie przewodnictwa, podczas gdy puste przestrzenie powstałe w wyniku braku elektronów, znane jako, działają jako nośniki w paśmie walencyjnym.
Półprzewodniki wykazują umiarkowaną przewodność, na którą wpływają takie czynniki, jak temperatura, oświetlenie światłem i zanieczyszczenia domieszkujące.

podstawy półprzewodników

Istnieją różnice w przewodności elektrycznej materiałów — metali, półprzewodników i izolatorów, które przedstawiono za pomocą diagramów pasm energetycznych.

Metale takie jak miedź (Cu), cynk (Zn) lub ołów (Pb) mają niską rezystywność i charakteryzują się pasmami przewodnictwa, które albo nie są w pełni zajęte, albo pokrywają się z pasmem walencyjnym, przez co pasmo wzbronione nie istnieje. Umożliwia to elektronom o najwyższych poziomach energii pasma walencyjnego łatwe przejście do pasma przewodnictwa po uzyskaniu minimalnej energii kinetycznej z przyłożonego pola elektrycznego. W rezultacie, przy wielu dostępnych stanach bliskich wypełnionym, metale ułatwiają przepływ prądu elektrycznego.

Półprzewodniki mają wypełnione pasmo walencyjne i puste pasmo przewodnictwa oddzielone małą przerwą wzbronioną, rzędu 1 eV, co pozwala na termiczne wzbudzenie niektórych elektronów walencyjnych do pasma przewodnictwa w temperaturze pokojowej. Powoduje to umiarkowaną liczbę nośników ładunku, dzięki czemu półprzewodniki są bardziej przewodzące niż izolatory, ale mniej niż metale. Energia pasma wzbronionego jest różna dla półprzewodników i wynosi 1,12 eV dla krzemu (Si) i 1,42 eV dla arsenku galu (GaAs).

W izolatorach takich jak SiO_2 pasmo walencyjne jest wypełnione elektronami, a pasmo przewodnictwa jest puste. Izolatory mają dużą przerwę wzbronioną, co utrudnia wzbudzenie elektronów walencyjnych przez pasmo przewodnictwa w temperaturze pokojowej. Dzieje się tak, ponieważ elektrony walencyjne w izolatorach biorą udział w silnych wiązaniach kowalencyjnych i do rozerwania wymagają znacznej energii. Duża przerwa energetyczna oddziela wypełnione pasma walencyjne i puste pasma przewodnictwa, a energia cieplna w temperaturze pokojowej jest niewystarczająca do wzbudzenia elektronów przez tę szczelinę. W rezultacie bardzo niewiele elektronów jest dostępnych do przewodzenia, a materiał nie może skutecznie przewodzić prądu elektrycznego.

Podstawy półprzewodników

Materiały są ogólnie podzielone na trzy typy: metale, izolatory i półprzewodniki.
Metale nie mają energetycznej przerwy energetycznej ze względu na nakładanie się ...

Education

JoVE Core

Electrical Engineering

Elektrotechnika

Unit 1

Jednostka 1

Basics of Semiconductors

KEY TERMS AND CONCEPTS

KLUCZOWE TERMINY I POJĘCIA

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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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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Conservation of Momentum

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Clarification statement: Emphasis is on the quantitative conservation of momentum in interactions and the qualitative meaning of this principle. 

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HS-PS2-2

Impulse

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Impulse-Momentum Theorem

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Collisions in Multiple Dimensions: Problem Solving

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Apply scientific and engineering ideas to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision. 

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Assessment Boundary: Assessment is limited to qualitative evaluations and/or algebraic manipulations.

HS-PS2-3

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Gravitation Between Spherically Symmetric Masses

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Coulomb's Law and The Principle of Superposition

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HS-PS2-4

Magnetic Fields

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Faraday's Law

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Lenz's Law

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Assessment Boundary: Assessment is limited to designing and conducting investigations with provided materials and tools.

HS-PS2-5

Bonding in Metals

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Band Theory

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Materials are broadly categorized into three types as metals, insulators, and semiconductors.
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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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