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

Unter Ladungsträgererzeugung versteht man die Erzeugung von Elektron-Loch-Paaren.
Die Band-zu-Band-Erzeugung erfolgt in Halbleitern mit direkter Bandlücke durch thermische Anregung oder Photonenabsorption. In solchen Halbleitern haben das Maximum des Valenzbandes und das Minimum des Leitungsbandes den gleichen Impuls.
Die indirekte Erzeugung von Ladungsträgern erfolgt durch die Absorption von Gitterenergie aus Phononen und ist dominant bei Halbleitern mit indirekter Bandlücke, bei denen das Valenzbandmaximum und das Leitungsbandminimum bei unterschiedlichen Impulsen liegen.
Bei der Schneckenerzeugung werden Ladungsträger erzeugt, indem die Energie eines hochenergetischen Teilchens verbraucht wird. Dieselben hochenergetischen Teilchen können mehrere Elektron-Loch-Paare erzeugen, indem sie das verfügbare hohe elektrische Feld während der Stoßionisation nutzen.
Im Gegensatz dazu ist die Rekombination der Prozess der Vernichtung von Elektronen und Löchern.
Bei der Band-zu-Band-Rekombination geht das Elektron vom Leitungs- in das Valenzband über und setzt ein Photon frei.
Bei der indirekten Rekombination werden lokalisierte Energiezustände, sogenannte Traps, für Übergänge zwischen dem Leitungs- und dem Valenzband verwendet, wodurch Energie als Wärme freigesetzt wird.
Bei der Auger-Rekombination handelt es sich um die Rekombination eines Elektrons und eines Lochs, wobei die resultierende Energie auf einen anderen Träger übertragen wird.

grundlagen der halbleiter

Carrier Generation and Recombination

Trägererzeugung ist der Prozess, durch den Elektronen-Loch-Paare (EHPs) innerhalb des Halbleiters erzeugt werden. In Halbleitern mit direkter Bandlücke, wie Galliumarsenid (GaAs), geschieht dies effizient, wenn Energieabsorption Valenzelektronen dazu veranlasst, in das Leitungsband zu springen und Löcher zurückzulassen.

Dieser Prozess wird durch die Erzeugungsrate G gegeben und ist aufgrund der Impulserhaltung zwischen dem Valenzbandmaximum und dem Leitungsbandminimum effizient.

Die indirekte Erzeugung beinhaltet einen Zwischenschritt und ist typisch für Halbleiter mit indirekter Bandlücke wie Silizium (Si). Halbleiter mit indirekter Bandlücke benötigen zusätzlichen Impuls von Phononen, wodurch die Trägererzeugung weniger effizient wird. Auger-Erzeugung und Stoßionisation erzeugen mehrere EHPs in energiereichen Umgebungen, wie starken elektrischen Feldern.

Rekombination ist der Prozess, der die Anzahl der freien Ladungsträger reduziert. Direkte Band-zu-Band-Rekombination tritt in Halbleitern wie Galliumarsenid auf, wo Elektronen und Löcher direkt ohne Zwischenzustände rekombinieren.

Die Rekombinationsrate für einen n-Typ-Halbleiter, bei dem Elektronen die Mehrheit der Ladungsträger sind, wird wie folgt angegeben:

<img alt="Equation 1" src="/files/ftp_upload/15154/15154_Equation_1.svg" style="text-align: center; height: 20px;">

Wobei B der Rekombinationskoeffizient und n und p die Konzentrationen von Elektronen bzw. Löchern sind. Indirekte Rekombination beinhaltet Fallen: lokalisierte Energiezustände innerhalb der Bandlücke. Ladungsträger werden vorübergehend von diesen Zuständen eingefangen und rekombinieren dann, wobei Energie als Wärme freigesetzt wird, ein nicht strahlender Prozess.

Das Gleichgewicht zwischen Erzeugung und Rekombination wird wie folgt beschrieben:

<img alt="Equation 2" src="/files/ftp_upload/15154/15154_Equation_2.svg" style="text-align: center; height: 20px;">

Unter Nichtgleichgewichtsbedingungen verursachen überschüssige Ladungsträger eine Netto-Rekombinationsrate U, die dazu neigt, das Gleichgewicht wiederherzustellen. Bei einer Injektion auf niedrigem Niveau, bei der die Minoritätsträgerkonzentration (Δp) deutlich niedriger ist als die Majoritätsträgerkonzentration, beträgt die Rate:

<img alt="Equation 3" src="/files/ftp_upload/15154/15154_Equation_3.svg" style="text-align: center; height: 18px;">

Trägererzeugungs- und Rekombinationsraten sind bei thermischem Gleichgewicht ausgeglichen. Wenn jedoch externe Kräfte wie Licht oder elektrische Felder dieses Gleichgewicht stören, gerät der Halbleiter in einen Nichtgleichgewichtszustand. Die Dynamik der Rückkehr zum Gleichgewicht beinhaltet komplexe Wechselwirkungen zwischen diesen Erzeugungs- und Rekombinationsmechanismen.

Grundlagen der Halbleiter

Unter Ladungsträgererzeugung versteht man die Erzeugung von Elektron-Loch-Paaren.
Die Band-zu-Band-Erzeugung erfolgt in Halbleitern mit direkter Bandlücke durch thermische Anregung ...

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JoVE Core

Electrical Engineering

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Unit 1

Einheit 1

Basics of Semiconductors

KEY TERMS AND CONCEPTS

ZENTRALE BEGRIFFE UND KONZEPTE

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

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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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