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

La jonction p-n à l’intérieur d’une LED nécessite une polarisation externe pour produire de la lumière.
La polarisation directe consiste à appliquer une tension aux bornes de la jonction p-n, la borne positive de la batterie étant connectée au côté p et la borne négative au côté n. La tension appliquée s’oppose au potentiel de jonction, réduisant la largeur de la barrière.
Cette largeur de barrière réduite permet le flux de courant en augmentant la diffusion de la porteuse majoritaire. Le courant de diffusion est supérieur au courant de dérive, et le courant net circule dans le sens aller de p à n.
Pendant la diffusion, la recombinaison des électrons et des trous dans la région de jonction émet des photons, ce qui fait briller la LED.
Dans le biais inverse, la borne positive de la batterie est connectée au côté n et la borne négative au côté p.
Cela empêche la LED de briller lorsque le potentiel appliqué s’ajoute au potentiel de jonction, ce qui entraîne une augmentation de la largeur de la barrière et une diminution de la diffusion de la porteuse majoritaire.
Le courant net est le faible courant de dérive obtenu grâce aux porteurs minoritaires.
Si la tension de polarisation inverse dépasse un certain seuil, une rupture de jonction se produit, entraînant un flux de courant important.

polarisation de la jonction p-n

Le fonctionnement d'une diode à jonction p-n implique diverses conditions de polarisation, notamment la polarisation directe, la polarisation inverse et l'équilibre.
À l’équilibre, aucune tension externe n’est appliquée aux bornes de la jonction p-n. La région d'appauvrissement se forme à l'interface de la jonction en raison de la diffusion des porteurs, qui laisse derrière elle des dopants chargés, des accepteurs du côté p et des donneurs du côté n. Ces charges immobiles créent un champ électrique qui empêche toute diffusion ultérieure des porteurs. Le diagramme de bande d'énergie associé montre que les niveaux de Fermi des deux côtés sont alignés, indiquant l'équilibre. Le potentiel intégré à travers la jonction empêche le flux net de transporteurs à travers la jonction.
Lorsque la diode est polarisée en direct, la tension appliquée réduit le potentiel de barrière et rétrécit la largeur de la région d'appauvrissement. En conséquence, les porteurs peuvent facilement traverser la jonction et le diagramme de bande correspondant montre les bandes d’énergie se courbant vers le haut, indiquant la réduction du potentiel de barrière. Le courant aux bornes de la diode sous polarisation directe augmente de façon exponentielle avec la tension appliquée.
En polarisation inverse, la tension externe est appliquée dans la direction opposée, élargissant la région d'appauvrissement, augmentant le potentiel de barrière, rendant difficile le passage des porteurs à la jonction et réduisant le flux de courant à un très faible courant de saturation inverse. Le diagramme de bandes d'énergie pour la polarisation inverse montre les bandes se courbant vers le bas, indiquant un potentiel de barrière accru. Le courant en polarisation inverse est une petite valeur constante. Il est proche du courant de saturation mais de signe opposé, reflétant le flux mineur de porteurs dû à la génération thermique dans la région d'épuisement.

Polarisation de la jonction P-N

La jonction p-n à l’intérieur d’une LED nécessite une polarisation externe pour produire de la lumière.
La polarisation directe consiste à appliquer une tension aux bornes de la jonction p-n avec le ...

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Basics of Semiconductors

Les bases des semi-conducteurs

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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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Explore equilibrium, forward bias, and reverse bias in a p-n junction diode, including depletion region changes, band diagrams, and current flow.

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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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