Name: semiconductor charge carriers: creation and loss
Uploaded: 2024-07-08T13:20:08.000Z
Duration: 1 min 22 s
Channel: JoVE

A geração de portadores refere-se à criação de pares de elétrons-buracos.
A geração de banda a banda ocorre em semicondutores de band gap direto por meio de excitação térmica ou absorção de fótons. Em tais semicondutores, o máximo da banda de valência e o mínimo da banda de condução têm o mesmo momento.
A geração indireta de portadores ocorre pela absorção de energia de rede de fônons e é dominante em semicondutores de bandgap indireto, que têm sua banda de valência máxima e banda de condução mínima em diferentes momentos.
Na geração Auger, os portadores são gerados consumindo a energia de uma partícula altamente energética. Essas mesmas partículas de alta energia podem gerar vários pares de elétrons-buracos usando o alto campo elétrico disponível durante a ionização por impacto.
Em contraste, a recombinação é o processo de aniquilação de elétrons e buracos.
Na recombinação banda a banda, o elétron faz a transição da condução para a banda de valência, liberando um fóton.
Durante a recombinação indireta, estados de energia localizados chamados armadilhas são utilizados para transições entre as bandas de condução e valência, liberando energia como calor.
A recombinação do Auger envolve a recombinação de um elétron e um buraco, transferindo a energia resultante para outro portador.

noções básicas de semicondutores

Carrier Generation and Recombination

A geração de portadora é o processo pelo qual pares elétron-buraco (EHPs) são criados dentro do semicondutor. Em semicondutores de bandgap direto, como o arsenieto de gálio (GaAs), isso ocorre de forma eficiente quando a absorção de energia faz com que os elétrons de valência saltem para a banda de condução, deixando para trás buracos.
Este processo é dado pela taxa de geração G e é eficiente devido à conservação do momento entre o máximo da banda de valência e o mínimo da banda de condução.
A geração indireta envolve uma etapa intermediária e é típica em semicondutores de bandgap indireto como o silício (Si). Os semicondutores de bandgap indireto requerem impulso adicional dos fônons, tornando a geração de portadora menos eficiente. A geração de Auger e a ionização por impacto produzem vários EHPs em ambientes de alta energia, como campos elétricos fortes.
A recombinação é o processo que reduz o número de operadoras gratuitas. A recombinação direta banda a banda ocorre em semicondutores como o arsenieto de gálio, onde elétrons e buracos se recombinam diretamente, sem estados intermediários.
A taxa de recombinação para um semicondutor do tipo n, onde os elétrons são os portadores majoritários, é dada por:
<img alt="Equation 1" src="/files/ftp_upload/15154/15154_Equation_1.svg" style="height: 20px;">
Onde B é o coeficiente de recombinação e n e p são as concentrações de elétrons e lacunas, respectivamente. A recombinação indireta envolve armadilhas: estados de energia localizados dentro do bandgap. Os portadores são temporariamente capturados por esses estados e depois se recombinam, liberando energia na forma de calor, um processo não radiativo.
O equilíbrio entre geração e recombinação é descrito por:
<img alt="Equation 2" src="/files/ftp_upload/15154/15154_Equation_2.svg" style="height: 20px;">
Em condições de não equilíbrio, o excesso de portadores causa uma taxa líquida de recombinação U, que tende a restaurar o equilíbrio. Na injeção de baixo nível, onde a concentração de portadores minoritários (Δp) é significativamente menor que a concentração de portadores majoritários, a taxa é:
<img alt="Equation 3" src="/files/ftp_upload/15154/15154_Equation_3.svg" style="height: 18px;">
A geração de portadores e as taxas de recombinação são equilibradas no equilíbrio térmico. No entanto, quando forças externas, como luz ou campos eléctricos, perturbam este equilíbrio, o semicondutor entra num estado de não equilíbrio. A dinâmica de retorno ao equilíbrio envolve interações complexas entre esses mecanismos de geração e recombinação.

Noções básicas de semicondutores

A geração de portadores refere-se à criação de pares de elétrons-buracos.
A geração de banda a banda ocorre em semicondutores de gap de banda direta por excitação térmica ...

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

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 conduction band. This works well when momentum is conserved between the valence band maximum and the conduction band minimum. Indirect generation is different and is common in indirect-bandgap semiconductors like silicon. It uses an intermediate step and needs extra momentum from phonons, so it is less efficient.

Some high-energy conditions can create more than one EHP. Auger generation and impact ionization both produce multiple electron-hole pairs, especially in strong electric fields. These processes show how carrier populations can rise quickly under extreme energy input.

Recombination removes free charge carriers. In direct band-to-band recombination, seen in materials like gallium arsenide, electrons and holes recombine directly without a middle state. For an n-type semiconductor, where electrons are the majority carriers, the recombination rate depends on the recombination coefficient B and on the electron and hole concentrations, n and p.

Indirect recombination uses traps, which are localized energy states inside the bandgap. Carriers can be captured by these states and then recombine later. This process releases energy as heat, so it is non-radiative.

At thermal equilibrium, generation and recombination are balanced. When light or an electric field pushes the semiconductor out of equilibrium, excess carriers create a net recombination rate U that works to restore balance. At low-level injection, where the minority carrier change Δp is much smaller than the majority carrier concentration, the recombination rate follows a simpler form. These interactions describe how semiconductors return to equilibrium after disturbance.

Semiconductor Charge Carriers: Creation and Loss

semiconductor-charge-carriers-creation-and-loss

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...

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carrier generation and recombination

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

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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 Diode Under Bias

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metal-semiconductor junctions

Schottky and Ohmic Metal Contacts

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biasing of metal-semiconductor junctions

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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

Learn how semiconductors create electron-hole pairs, lose carriers through recombination, and return to equilibrium after light or electric field changes.

Semiconductor Charge Carriers: Creation and Loss | 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

Semiconductor Charge Carriers: Creation and Loss

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