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

La generazione di portatori si riferisce alla creazione di coppie elettrone-lacuna.
La generazione da banda a banda avviene nei semiconduttori a banda proibita diretta tramite eccitazione termica o assorbimento di fotoni. In tali semiconduttori, il massimo della banda di valenza e il minimo della banda di conduzione hanno lo stesso momento.
La generazione indiretta di portatori avviene assorbendo energia reticolare dai fononi ed è dominante nei semiconduttori a banda proibita indiretta, che hanno il massimo della banda di valenza e il minimo della banda di conduzione in momenti diversi.
Nella generazione Auger, i vettori sono generati consumando l'energia di una particella altamente energetica. Queste stesse particelle ad alta energia possono generare più coppie elettrone-lacuna utilizzando l'elevato campo elettrico disponibile durante la ionizzazione da impatto.
Al contrario, la ricombinazione è il processo di annichilazione di elettroni e lacune.
Nella ricombinazione banda-banda, l'elettrone passa dalla banda di conduzione a quella di valenza, rilasciando un fotone.
Durante la ricombinazione indiretta, gli stati energetici localizzati chiamati trappole vengono utilizzati per le transizioni tra le bande di conduzione e di valenza, rilasciando energia sotto forma di calore.
La ricombinazione Auger comporta la ricombinazione di un elettrone e di una lacuna, trasferendo l'energia risultante a un altro vettore.

nozioni di base sui semiconduttori

Carrier Generation and Recombination

La generazione del portatore è il processo mediante il quale vengono create coppie elettrone-lacuna (EHP) all'interno del semiconduttore. Nei semiconduttori a banda proibita diretta, come l'arseniuro di gallio (GaAs), ciò avviene in modo efficiente quando l'assorbimento di energia spinge gli elettroni di valenza a saltare nella banda di conduzione, lasciando dietro di sé lacune.

Questo processo è dato dalla velocità di generazione G ed è efficiente grazie alla conservazione della quantità di moto, tra il massimo della banda di valenza e il minimo della banda di conduzione.

La generazione indiretta prevede un passaggio intermedio ed è tipica dei semiconduttori con banda proibita indiretta come il silicio (Si). I semiconduttori con banda proibita indiretto, richiedono ulteriore slancio da parte dei fononi, rendendo la generazione di portanti meno efficiente. La generazione di coclee e la ionizzazione per impatto, producono più EHP in ambienti ad alta energia, come forti campi elettrici.

La ricombinazione è il processo che riduce il numero di portatori gratuiti. La ricombinazione diretta banda-banda avviene nei semiconduttori come l'arseniuro di gallio, dove elettroni e lacune si ricombinano direttamente senza stati intermedi.

La velocità di ricombinazione per un semiconduttore di tipo n, dove gli elettroni sono i portatori maggioritari, è data da:

<img alt="Equation 1" src="/files/ftp_upload/15154/15154_Equation_1.svg" style="height: 20px;">

Dove B è il coefficiente di ricombinazione e n e p sono rispettivamente le concentrazioni di elettroni e lacune. La ricombinazione indiretta coinvolge trappole: stati energetici localizzati all'interno della banda proibita. I portatori vengono temporaneamente catturati da questi stati e poi si ricombinano, rilasciando energia sotto forma di calore, un processo non radiativo.

L’equilibrio tra generazione e ricombinazione è descritto da:

<img alt="Equation 2" src="/files/ftp_upload/15154/15154_Equation_2.svg" style="height: 20px;">

In condizioni di non equilibrio, i portatori in eccesso provocano un tasso di ricombinazione netto U, che tende a ripristinare l'equilibrio. All'iniezione a basso livello, dove la concentrazione del portatore minoritario (Δp), è significativamente inferiore alla concentrazione del portatore maggioritario, la velocità è:

<img alt="Equation 3" src="/files/ftp_upload/15154/15154_Equation_3.svg" style="height: 18px;">

Le velocità di generazione e ricombinazione dei portatori sono bilanciate all'equilibrio termico. Tuttavia, quando forze esterne come la luce o i campi elettrici disturbano questo equilibrio, il semiconduttore entra in uno stato di non equilibrio. Le dinamiche del ritorno all'equilibrio implicano interazioni complesse tra questi meccanismi di generazione e ricombinazione.

Nozioni di Base sui Semiconduttori

La generazione di portatori si riferisce alla creazione di coppie elettrone-lacuna.
La generazione da banda a banda avviene nei semiconduttori a banda proibita diretta tramite eccitazione termica ...

Education

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JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

Basics of Semiconductors

Fondamenti dei semiconduttori

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

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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

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biasing of p-n junction

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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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