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

Der p-n-Übergang innerhalb einer LED erfordert eine externe Vorspannung, um Licht zu erzeugen.
Bei der Vorwärtsvorspannung wird eine Spannung über den p-n-Übergang angelegt, wobei der Pluspol der Batterie mit der p-Seite und der Minuspol mit der n-Seite verbunden ist. Die angelegte Spannung steht dem Sperrschichtpotenzial entgegen, wodurch sich die Sperrbreite verringert.
Diese reduzierte Barrierebreite ermöglicht den Stromfluss durch Erhöhung der Mehrheitsträgerdiffusion. Der Diffusionsstrom ist höher als der Driftstrom, und der Nettostrom fließt in Durchlassrichtung von p nach n.
Während der Diffusion werden durch die Rekombination von Elektronen und Löchern im Sperrschichtbereich Photonen emittiert, die die LED zum Leuchten bringen.
Bei der Sperrvorspannung wird der Pluspol der Batterie mit der n-Seite und der Minuspol mit der p-Seite verbunden.
Dadurch wird verhindert, dass die LED leuchtet, da das angelegte Potential zum Sperrschichtpotenzial hinzukommt, was zu einer erhöhten Barrierebreite und einer verringerten Mehrheitsträgerdiffusion führt.
Der Nettostrom ist der kleine Driftstrom, der aufgrund von Minoritätsträgern erhalten wird.
Wenn die Sperrspannung einen bestimmten Schwellenwert überschreitet, kommt es zu einem Durchschlag der Sperrschicht, was zu einem großen Stromfluss führt.

vorspannung des p-n-Übergangs

Der Betrieb einer P-N-Übergangsdiode umfasst verschiedene Vorspannungsbedingungen, darunter Vorwärtsvorspannung, Rückwärtsvorspannung und Gleichgewicht.

Im Gleichgewicht wird keine externe Spannung über den P-N-Übergang angelegt. Die Verarmungszone wird an der Übergangsschnittstelle aufgrund der Diffusion von Trägern gebildet, die geladene Dotierstoffe, Akzeptoren auf der P-Seite und Donatoren auf der N-Seite hinterlassen. Diese unbeweglichen Ladungen erzeugen ein elektrisches Feld, das eine weitere Diffusion von Trägern verhindert. Das zugehörige Energiebanddiagramm zeigt, dass die Fermi-Niveaus auf beiden Seiten ausgerichtet sind, was auf Gleichgewicht hinweist. Das eingebaute Potenzial über dem Übergang verhindert den Nettofluss von Trägern über den Übergang.

Wenn die Diode in Vorwärtsrichtung vorgespannt ist, verringert die angelegte Spannung das Sperrpotenzial und verengt die Breite der Verarmungszone. Infolgedessen können Träger den Übergang leicht überqueren, und das entsprechende Banddiagramm zeigt, dass sich die Energiebänder nach oben biegen, was auf die Verringerung des Sperrpotenzials hinweist. Der Strom durch die Diode bei Vorwärtsvorspannung steigt exponentiell mit der angelegten Spannung.

Bei Sperrvorspannung wird die externe Spannung in die entgegengesetzte Richtung angelegt, wodurch die Verarmungszone erweitert und das Sperrpotential erhöht wird, wodurch es für Ladungsträger schwieriger wird, die Verbindung zu überqueren, und der Stromfluss auf einen sehr kleinen Sperrsättigungsstrom reduziert wird. Das Energiebanddiagramm bei Sperrvorspannung zeigt, dass sich die Bänder nach unten biegen, was auf ein erhöhtes Sperrpotential hinweist. Der Strom bei Sperrvorspannung ist ein kleiner konstanter Wert. Er liegt nahe am Sättigungsstrom, hat jedoch das entgegengesetzte Vorzeichen, was den geringen Ladungsträgerfluss aufgrund der Wärmeerzeugung innerhalb der Verarmungszone widerspiegelt.

Vorspannung des P-N-Übergangs

Der p-n-Übergang innerhalb einer LED erfordert eine externe Vorspannung, um Licht zu erzeugen.
Bei der Vorwärtsvorspannung wird eine Spannung über den p-n-Übergang mit dem ...

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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

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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...

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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.

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P-N Junction Diode Under Bias

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