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

La giunzione pn all'interno di un LED richiede una polarizzazione esterna per produrre luce.
La polarizzazione diretta comporta l'applicazione di una tensione attraverso la giunzione p-n con il terminale positivo della batteria collegato al lato p e il terminale negativo al lato n. La tensione applicata si oppone al potenziale di giunzione, riducendo la larghezza della barriera.
Questa larghezza ridotta della barriera consente il flusso di corrente aumentando la diffusione della portante maggioritaria. La corrente di diffusione è superiore alla corrente di deriva e la corrente netta scorre in avanti da p a n.
Durante la diffusione, la ricombinazione di elettroni e lacune nella regione della giunzione emette fotoni, facendo brillare il LED.
Nella polarizzazione inversa, il terminale positivo della batteria è collegato al lato n e il negativo al lato p.
Ciò impedisce al LED di brillare poiché il potenziale applicato si aggiunge al potenziale di giunzione, con conseguente aumento della larghezza della barriera e diminuzione della diffusione della portante maggioritaria.
La corrente netta è la piccola corrente di deriva ottenuta a causa di portatori di minoranza.
Se la tensione di polarizzazione inversa supera una certa soglia, si verifica la rottura della giunzione, con conseguente flusso di corrente elevato.

polarizzazione della giunzione p-n

Il funzionamento di un diodo a giunzione pn, coinvolge varie condizioni di polarizzazione, tra cui polarizzazione diretta, polarizzazione inversa ed equilibrio.

In equilibrio, nessuna tensione esterna viene applicata attraverso la giunzione p-n. La regione di svuotamento si forma sull'interfaccia di giunzione a causa della diffusione dei portatori, che lascia dietro di sé droganti carichi, accettori sul lato p e donatori sul lato n. Queste cariche immobili creano un campo elettrico che impedisce l'ulteriore diffusione dei portatori. Il relativo diagramma delle bande di energia, mostra che i livelli di Fermi su entrambi i lati sono allineati, indicando l'equilibrio. Il potenziale incorporato attraverso la giunzione impedisce il flusso netto di portanti attraverso la giunzione.


Quando il diodo è polarizzato direttamente, la tensione applicata riduce il potenziale di barriera e restringe la larghezza della regione di svuotamento. Di conseguenza, i portatori possono facilmente attraversare la giunzione e il diagramma a bande corrispondente, mostra le bande di energia che si piegano verso l'alto, indicando la riduzione del potenziale di barriera. La corrente attraverso il diodo sotto polarizzazione diretta, aumenta esponenzialmente con la tensione applicata.

Nella polarizzazione inversa, la tensione esterna viene applicata nella direzione opposta, allargando la regione di svuotamento, aumentando il potenziale di barriera, rendendo difficile l'attraversamento della giunzione da parte dei portatori e riducendo il flusso di corrente a una corrente di saturazione inversa molto piccola. Il diagramma delle bande di energia per la polarizzazione inversa, mostra le bande che si piegano verso il basso, indicando un aumento del potenziale di barriera. La corrente in polarizzazione inversa è un piccolo valore costante. È vicina alla corrente di saturazione ma di segno opposto, riflettendo il minor flusso di portatori dovuto alla generazione termica all'interno della regione di svuotamento.

Polarizzazione della Giunzione P-N

La giunzione pn all'interno di un LED richiede una polarizzazione esterna per produrre luce.
La polarizzazione diretta comporta l'applicazione di una tensione attraverso la giunzione p-n con il ...

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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.

electrical engineering

P-N Junction Diode Under Bias

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