Name: vacuum level and schottky barriers
Uploaded: 2024-07-08T13:20:09.000Z
Duration: 1 min 12 s
Channel: JoVE

O nível de vácuo representa o limite de energia para um elétron escapar da superfície de um material. Normalmente fica acima da banda de condução de um semicondutor e serve como referência para as energias dos elétrons.
Em semicondutores, a afinidade eletrônica é a lacuna de energia entre o mínimo da banda de condução e o nível de vácuo.
A função de trabalho é a energia mínima necessária para liberar um elétron do nível de Fermi para o nível de vácuo e depende do material.
Os metais exibem altas funções de trabalho, em torno de 2 a 5 eV, devido aos seus estados densos de nível de Fermi.
Os semicondutores exibem funções de trabalho variáveis à medida que seus níveis de Fermi mudam, influenciados pela dopagem e temperatura.
Um metal e um semicondutor em contato atingem o equilíbrio, criando um nível de vácuo contínuo através da junção.
Simultaneamente, a transferência de carga continua até que os níveis de Fermi se alinhem, causando flexão da banda de energia no semicondutor e formando uma barreira Schottky.
A altura da barreira da junção é determinada pela função de trabalho do metal e pela afinidade eletrônica do semicondutor.

dinâmica do nível de fermi

O nível de vácuo denota o limite de energia necessário para um elétron escapar da superfície de um material. Geralmente é posicionado acima da banda de condução de um semicondutor e atua como referência para comparar energias eletrônicas em vários materiais.
A afinidade eletrônica em semicondutores refere-se à lacuna de energia entre o mínimo de sua banda de condução e o nível de vácuo e é um parâmetro crítico para determinar a facilidade com que um semicondutor pode aceitar elétrons adicionais.
A função trabalho representa a menor quantidade de energia necessária para mover um elétron do nível de Fermi, que é o nível de energia onde um elétron tem 50% de chance de estar presente, para o nível de vácuo. Este valor varia entre os materiais, com os metais normalmente apresentando altas funções de trabalho variando de 2 a 5 eV, atribuídas aos seus níveis de Fermi densamente povoados.
Os semicondutores, por outro lado, exibem funções de trabalho dinâmicas devido à natureza variável de seus níveis de Fermi, influenciados por fatores como dopagem e mudanças de temperatura.
Quando um metal e um semicondutor entram em contato, eles buscam o equilíbrio, levando a um nível de vácuo uniforme através da junção através da transferência de carga, continuando até que os níveis de Fermi de ambos os materiais se alinhem. Isso desencadeia a curvatura da banda de energia dentro do semicondutor, levando à criação de uma barreira Schottky, uma barreira de energia potencial para os elétrons que se movem através da junção metal-semicondutor.
A altura da barreira Schottky governa a condutividade da junção e é determinada pela relação entre a função de trabalho do metal e a afinidade eletrônica do semicondutor.

Dinâmica do Nível de Fermi

O nível de vácuo representa o limite de energia para um elétron escapar da superfície de um material. Normalmente fica acima de um semicondutor ...

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

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 move an electron from the Fermi level, the level where an electron has a 50% chance of being present, to the vacuum level.

Work function values are not the same for every material. Metals usually have high work functions, often between 2 and 5 eV, because their Fermi levels are densely filled. Semiconductors have work functions that can change. Doping and temperature both affect their Fermi levels.

When a metal touches a semiconductor, the two materials move toward equilibrium. Charge transfer continues until their Fermi levels line up and the vacuum level becomes uniform across the junction. This process bends the energy bands in the semiconductor and forms a Schottky barrier, which is a potential energy barrier for electrons crossing the metal-semiconductor junction.

The height of the Schottky barrier controls how well the junction conducts. It depends on the metal’s work function and the semiconductor’s electron affinity. This relationship is key to understanding electron flow at metal-semiconductor contacts.

Vacuum Level and Schottky Barriers

energy bands in solids

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semiconductors

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types of semiconductors

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carrier transport

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p-n junction

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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

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metal-semiconductor junctions

Schottky and Ohmic Metal Contacts

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biasing of metal-semiconductor junctions

How Bias Changes Metal-Semiconductor Current

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fermi level

Fermi Level in Semiconductors

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fermi level dynamics

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

Explore vacuum level, electron affinity, work function, and Schottky barriers. Learn how metal-semiconductor contacts align energy levels and affect conductivity.

Vacuum Level and Schottky Barriers | 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

Vacuum Level and Schottky Barriers

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