Name: p-n junction diode under bias
Uploaded: 2025-05-22T09:06:15.000Z
Duration: 1 min 16 s
Channel: JoVE

A junção pn dentro de um LED requer polarização externa para produzir luz.
A polarização direta envolve a aplicação de uma tensão na junção pn com o terminal positivo da bateria conectado ao lado p e o terminal negativo ao lado n. A tensão aplicada se opõe ao potencial de junção, reduzindo a largura da barreira.
Essa largura de barreira reduzida permite o fluxo de corrente aumentando a difusão da portadora majoritária. A corrente de difusão é maior do que a corrente de deriva e a corrente líquida flui na direção direta de p a n.
Durante a difusão, a recombinação de elétrons e buracos na região de junção emite fótons, fazendo o LED brilhar.
Na polarização reversa, o terminal positivo da bateria é conectado ao lado n e o negativo ao lado p.
Isso evita que o LED brilhe à medida que o potencial aplicado aumenta o potencial de junção, resultando em uma largura de barreira aumentada e uma difusão de portadora majoritária diminuída.
A corrente líquida é a pequena corrente de deriva obtida devido a portadores minoritários.
Se a tensão de polarização reversa exceder um certo limite, ocorre a quebra da junção, resultando em um grande fluxo de corrente.

polarização da junção pn

A operação de um diodo de junção pn envolve várias condições de polarização, incluindo polarização direta, polarização reversa e equilíbrio.
Em equilíbrio, nenhuma tensão externa é aplicada através da junção pn. A região de depleção é formada na interface de junção devido à difusão de transportadores, que deixa para trás dopantes carregados, aceitadores no lado p e doadores no lado n. Essas cargas imóveis criam um campo elétrico que impede a difusão adicional de portadores. O diagrama de bandas de energia relacionado mostra que os níveis de Fermi em ambos os lados estão alinhados, indicando equilíbrio. O potencial incorporado através da junção impede o fluxo líquido de portadores através da junção.
Quando o diodo é polarizado diretamente, a tensão aplicada reduz o potencial da barreira e estreita a largura da região de depleção. Como resultado, os portadores podem facilmente cruzar a junção, e o diagrama de bandas correspondente mostra as bandas de energia curvando-se para cima, indicando a redução do potencial de barreira. A corrente através do diodo sob polarização direta aumenta exponencialmente com a tensão aplicada.
Na polarização reversa, a tensão externa é aplicada na direção oposta, ampliando a região de depleção, aumentando o potencial de barreira, dificultando a passagem dos portadores pela junção e reduzindo o fluxo de corrente para uma corrente de saturação reversa muito pequena. O diagrama de bandas de energia para polarização reversa mostra as bandas curvando-se para baixo, indicando aumento do potencial de barreira. A corrente em polarização reversa é um pequeno valor constante. Está próximo da corrente de saturação, mas com sinal oposto, refletindo o menor fluxo de portadores devido à geração térmica na região de depleção.

Polarização da junção PN

A junção pn dentro de um LED requer polarização externa para produzir luz.
A polarização direta envolve a aplicação de uma tensão através da junção pn com o ...

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

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 in balance. A built-in potential also exists across the junction. This potential prevents a net flow of carriers from one side to the other.

When the diode is forward biased, the applied voltage lowers the barrier potential. It also narrows the depletion region. Carriers can then cross the junction more easily. The band diagram shows the energy bands bending upward, which matches the reduced barrier.

Forward bias also causes the current to rise quickly as the applied voltage increases. The current increases exponentially with voltage. In reverse bias, the external voltage is applied in the opposite direction. The depletion region widens, the barrier potential increases, and carrier flow becomes very small.

The reverse-bias band diagram shows the energy bands bending downward. This change reflects the higher barrier potential. The current falls to a small reverse saturation current. It stays close to that saturation value and has the opposite sign, because only a minor carrier flow remains from thermal generation within the depletion region.

P-N Junction Diode Under Bias

energy bands in solids

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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...

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Semiconductor Charge Carriers: Creation and Loss

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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 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

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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

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key terms and concepts

Explore equilibrium, forward bias, and reverse bias in a p-n junction diode, including depletion region changes, band diagrams, and current flow.

P-N Junction Diode Under Bias | 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

P-N Junction Diode Under Bias

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