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

Os materiais são amplamente categorizados em três tipos como metais, isolantes e semicondutores.
Os metais não têm band gap de energia devido à sobreposição das bandas de valência e condução. Isso permite o livre movimento de elétrons, tornando os metais excelentes condutores de eletricidade.
Em contraste, os isoladores têm um grande intervalo de banda de energia, normalmente maior que 3 eV. À temperatura ambiente, nenhuma condução ocorre porque a energia térmica ou o campo elétrico aplicado são insuficientes para promover um número significativo de elétrons da banda de valência para a banda de condução, tornando-os maus condutores.
Semicondutores convencionais como o silício exibem um estreito intervalo de banda de energia em torno de 1,1 eV. À temperatura ambiente, um número significativo de elétrons pode ser excitado termicamente da banda de valência para a banda de condução, resultando em uma pequena corrente.
Essa transição gera operadoras. Os elétrons livres atuam como portadores na banda de condução, enquanto os vazios criados pela ausência de elétrons, conhecidos como buracos, atuam como portadores na banda de valência.
Os semicondutores exibem condutividade moderada, influenciada por fatores como temperatura, iluminação da luz e impurezas dopantes.

noções básicas de semicondutores

Há variação na condutividade elétrica dos materiais – metais, semicondutores e isolantes que são apresentados com a ajuda dos diagramas de bandas de energia.
Metais como cobre (Cu), zinco (Zn) ou chumbo (Pb) têm baixa resistividade e apresentam bandas de condução que não estão totalmente ocupadas ou se sobrepõem à banda de valência, tornando inexistente o bandgap. Isso permite que os elétrons nos níveis de energia mais altos da banda de valência transitem facilmente para a banda de condução ao ganharem energia cinética mínima de um campo elétrico aplicado. Como resultado, com muitos estados disponíveis próximos aos preenchidos, os metais facilitam o fluxo da corrente elétrica.
Os semicondutores têm uma banda de valência preenchida e uma banda de condução vazia separada por um pequeno intervalo de banda, da ordem de 1 eV, permitindo que alguns elétrons de valência sejam excitados termicamente para a banda de condução à temperatura ambiente. Isso resulta em um número moderado de portadores de carga, tornando os semicondutores mais condutores que os isolantes, mas menos que os metais. A energia do band gap varia para semicondutores, como 1,12 eV para silício (Si) e 1,42 eV para arsenieto de gálio (GaAs).
Em isolantes como o SiO2, a banda de valência está preenchida com elétrons e a banda de condução está vazia. Os isoladores têm um grande gap de banda, dificultando a excitação dos elétrons de valência pela banda de condução à temperatura ambiente. Isso ocorre porque os elétrons de valência nos isolantes estão envolvidos em fortes ligações covalentes e requerem energia significativa para serem quebrados. Uma grande lacuna de energia separa as bandas de valência preenchidas e de condução vazias, e a energia térmica à temperatura ambiente é insuficiente para excitar os elétrons através desta lacuna. Como resultado, muito poucos elétrons estão disponíveis para condução e o material não consegue conduzir a corrente elétrica de maneira eficaz.

Noções básicas de semicondutores

Os materiais são amplamente categorizados em três tipos como metais, isolantes e semicondutores.
Os metais não têm band gap de energia devido à sobreposição do ...

Education

JoVE Core

Electrical Engineering

Engenharia Elétrica

Unit 1

Unidade 1

Basics of Semiconductors

Fundamentos de Semicondutores

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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

Newton&#39;s second law is closely related to his first law of motion. It mathematically gives the cause-and-effect relationship between force and changes ...

Force and Acceleration

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Second Law: Motion under Same Force

Newton&#39;s laws can be applied to bodies at rest and bodies in motion. Newton&#39;s first law is applied to bodies in equilibrium, whereas the second ...

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

Conservation of Momentum: Introduction

The total momentum of a system consisting of N interacting objects is constant in time or is conserved. A system must meet two requirements for its ...

Conservation of Momentum

Conservation of Momentum: Problem Solving

Solving problems using the conservation of momentum requires four basic steps:

	Identify a closed system, where the total mass is constant, and no net ...

Conservation of Angular Momentum

A system&#39;s total angular momentum remains constant if the net external torque acting on the system is zero. Considering a system that consists of n ...

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Conservation of Angular Momentum: Application

A system&#39;s total angular momentum remains constant if the net external torque acting on the system is zero. Examples of such systems include a freely ...

Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system. 

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

Assessment Boundary: Assessment is limited to systems of two macroscopic bodies moving in one dimension.

HS-PS2-2

Impulse

According to Newton&#8217;s second law of motion, the rate of change of the momentum of an object is the net external force acting on it. The total change ...

Impulse-Momentum Theorem

The total change in the motion of an object is proportional to the total force vector acting on it and the time over which it acts. This product is called ...

Types Of Collisions - I

When two objects come in direct contact with each other, it is called a collision. During a collision, two or more objects exert forces on each other in a ...

Types of Collisions - II

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Elastic Collisions: Introduction

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Elastic Collisions: Case Study

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collisions-in-multiple-dimensions-introduction

Collisions in Multiple Dimensions: Introduction

It is far more common for collisions to occur in two dimensions; that is, the initial velocity vectors are neither parallel nor antiparallel to each ...

collisions-in-multiple-dimensions-problem-solving

Collisions in Multiple Dimensions: Problem Solving

In multiple dimensions, the conservation of momentum applies in each direction independently. Hence, to solve collisions in multiple dimensions, we should ...

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

Clarification statement: Examples of evaluation and refinement could include determining the success of the device at protecting an object from damage and modifying the design to improve it. Examples of a device could include a football helmet or a parachute. 

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

HS-PS2-3

Gravitation

In the years before Newton, a general belief prevailed that different laws governed objects in the sky than objects on Earth. When Kepler wrote down the ...

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Newton's Law of Gravitation

Our everyday observation tells us that all objects close to the Earth naturally tend to fall to the ground. Early philosophers assumed that this downward ...

gravitation-between-spherically-symmetric-masses

Gravitation Between Spherically Symmetric Masses

The gravitational potential energy between two spherically symmetric bodies can be calculated from the masses and the distance between the bodies, ...

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Coulomb's Law

Experiments with electric charges have shown that if two objects each have an electric charge, they exert an electric force on each other. The magnitude ...

coulomb-s-law-and-the-principle-of-superposition

Coulomb's Law and The Principle of Superposition

Coulomb&#39;s Law describes the force experienced by two point charges under each other&#39;s presence. But what if there are more than two charges? For ...

comparison-between-electrical-and-gravitational-forces

Comparison Between Electrical And Gravitational Forces

There are four fundamental forces in nature: the gravitational force, the electromagnetic force, the strong nuclear force, and the weak nuclear force. To ...

Newton's Law of Universal Gravitation

Source: Ketron Mitchell-Wynne, PhD,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of ...

Use mathematical representations of Newton's Law of Gravitation and Coulomb's Law to describe and predict the gravitational and electrostatic forces between objects. 

Clarification statement: Emphasis is on both quantitative and conceptual descriptions of gravitational and electric fields. 

Assessment Boundary: Assessment is limited to systems with two objects.

HS-PS2-4

Magnetic Fields

A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on ...

Electromagnetic Fields

Electric fields generated by static charges, often referred to as electrostatic fields, are characteristically different from electric fields created by ...

Maxwell's Equation Of Electromagnetism

James Clerk Maxwell (1831&#x2013;1879) was one of the major contributors to physics in the nineteenth century. Although he died young, he made major ...

Symmetry in Maxwell's Equations

Once the fields have been calculated using Maxwell&#x27;s four equations, the Lorentz force equation gives the force that the fields exert on a charged ...

Induction

An emf is induced when the magnetic field in a coil is changed by pushing a bar magnet into or out of the coil. emfs of opposite signs are produced by ...

Faraday's Law

Faraday&#39;s law state that the induced emf is the negative change in the magnetic flux per unit of time. Any change in the magnetic field or change in ...

Lenz's Law

The direction in which the induced emf drives the current around a wire loop can be found through the negative sign. However, it is usually easier to ...

Charge and Current

Charge, an inherent property of matter, is responsible for a wide range of electric phenomena. The SI unit of charge is the coulomb.
All matter comprises ...

Ohm's Law

Resistors, often made from metallic alloys or carbon compounds, model a material&#x27;s current-resisting behavior.
Ohm&#x27;s law states that the voltage ...

Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current. 

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

HS-PS2-5

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

Band Theory

When two or more atoms come together to form a molecule, their atomic orbitals combine and molecular orbitals of distinct energies result. In a solid, ...

Materials are broadly categorized into three types as metals, insulators, and semiconductors.
Metals have no energy band gap due to the overlap of the ...

Conductors and Insulators

Some materials may easily let electrical charges pass through them, while others obstruct their flow. The former are called conductors and the latter ...

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

Clarification statement: Emphasis is on the attractive and repulsive forces that determine the functioning of the material. Examples could include why electrically conductive materials are often made of metal, flexible but durable materials are made up of long chained molecules, and pharmaceuticals are designed to interact with specific receptors. 

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

Energy Bands in Metals and Insulators

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