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

K12 Standards

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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

Malzemeler genel olarak metaller, yalıtkanlar ve yarı iletkenler olarak üç türe ayrılır.
Metaller, değerlik ve iletim bantlarının üst üste binmesi nedeniyle enerji bandı aralığına sahip değildir. Bu, serbest elektron hareketine izin vererek metalleri mükemmel elektrik iletkenleri yapar.
Buna karşılık, yalıtkanlar, tipik olarak 3 eV'den daha büyük olan büyük bir enerji bandı aralığına sahiptir. Ortam sıcaklığında, termal enerji veya uygulanan elektrik alanı, değerlik bandından iletim bandına önemli sayıda elektronu teşvik etmek için yetersiz olduğu için iletim meydana gelmez ve bu da onları zayıf iletkenler yapar.
Silikon gibi geleneksel yarı iletkenler, 1.1 eV civarında dar bir enerji bandı aralığı sergiler. Ortam sıcaklığında, önemli sayıda elektron, değerlik bandından iletim bandına termal olarak uyarılabilir ve bu da küçük bir akıma neden olur.
Bu geçiş taşıyıcılar oluşturur. Serbest elektronlar iletim bandında taşıyıcı görevi görürken, delik olarak bilinen elektron yokluğunun yarattığı boşluklar değerlik bandında taşıyıcı görevi görür.
Yarı iletkenler, sıcaklık, ışık aydınlatması ve katkı maddesi safsızlıkları gibi faktörlerden etkilenen orta düzeyde iletkenlik sergiler.

yarı İletkenlerin temelleri

Enerji bant diyagramlarının yardımıyla gösterilen malzemelerin (metaller, yarı iletkenler ve yalıtkanlar) elektriksel iletkenliğinde farklılıklar vardır.
Bakır (Cu), çinko (Zn) veya kurşun (Pb) gibi metaller düşük dirençlidir ve iletim bantları ya tam olarak dolmaz ya da valans bandıyla örtüşür, bu da bant aralığını ortadan kaldırır. Bu, valans bandının en yüksek enerji seviyelerindeki elektronların, uygulanan bir elektrik alanından minimum kinetik enerji kazanması üzerine kolayca iletim bandına geçmesine olanak tanır. Sonuç olarak, dolu duruma yakın birçok mevcut durumla metaller, elektrik akımının kolay akışını kolaylaştırır.
Yarıiletkenler, bazı değerlik elektronlarının oda sıcaklığında iletim bandına termal olarak uyarılmasına izin veren, 1 eV düzeyinde küçük bir bant aralığıyla ayrılmış dolu bir değerlik bandına ve boş bir iletken bandına sahiptir. Bu, yarı iletkenleri yalıtkanlardan daha iletken, ancak metallerden daha az iletken hale getiren makul sayıda yük taşıyıcıyla sonuçlanır. Bant aralığı enerjisi yarı iletkenler için değişir; silikon (Si) için 1,12 eV ve galyum arsenit (GaAs) için 1,42 eV gibi.
SiO_2 gibi yalıtkanlarda değerlik bandı elektronlarla doludur, iletim bandı ise boştur. Yalıtkanların geniş bir bant aralığı vardır, bu da değerlik elektronlarının oda sıcaklığında iletim bandı tarafından uyarılmasını zorlaştırır. Bunun nedeni, yalıtkanlardaki değerlik elektronlarının güçlü kovalent bağlarda yer alması ve kırılması için önemli miktarda enerji gerektirmesidir. Dolu değerlik ve boş iletim bantlarını büyük bir enerji boşluğu ayırır ve oda sıcaklığındaki termal enerji, elektronları bu boşluk boyunca uyarmak için yetersizdir. Sonuç olarak iletim için çok az elektron kalır ve malzeme elektrik akımını etkili bir şekilde iletemez.

Yarı İletkenlerin Temelleri

Malzemeler genel olarak metaller, yalıtkanlar ve yarı iletkenler olarak üç türe ayrılır.
Metallerin üst üste binmesi nedeniyle enerji bandı aralığı yoktur ...

Education

JoVE Core

Electrical Engineering

Elektrik Mühendisliği

Unit 1

Ünite 1

Basics of Semiconductors

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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 Elektrik Mühendisliği, devre analizi teknikleriyle birlikte elektrik devrelerinin temel kavramlarını kapsayan, anlaşılması kolay animasyonlu videolar sunar. Operasyonel amplifikatörler ve devre dönüşümü kavramlarını kullanarak birinci dereceden ve ikinci dereceden devreleri içerir. Pratik tasarım örneklerinin ve gerçek dünya uygulamalarının bilim insanlarınca hazırlanan videolar aracılığıyla dahil edilmesi, karmaşık kavramları erişilebilir hale getirerek önemli bir eğitim değeri katmaktadır.

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HS-PS2-5

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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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