Name: p-n junction depletion region
Uploaded: 2024-07-08T13:20:08.000Z
Duration: 1 min 11 s
Channel: JoVE

Les lampadaires solaires fonctionnent indépendamment sans avoir besoin d’une alimentation externe, car ils contiennent des jonctions p-n dans leurs cellules solaires.
Une jonction p-n est formée en ajoutant des impuretés pentavalentes à une fine feuille de silicium de type p, en convertissant une partie de celle-ci en silicium de type n.
Le gradient de concentration des porteurs de charge des deux côtés de la feuille de silicium conduit à la diffusion des trous du côté p vers le côté n et des électrons du côté n vers le côté p, générant un courant de diffusion.
La région près de la jonction devient dépourvue de transporteurs de charge gratuite, formant la région d’appauvrissement. De plus, des charges positives et négatives liées au net restent dans cette région, créant un champ électrique et une différence de potentiel à travers la jonction.
Le champ électrique fait dériver les porteurs minoritaires dans la jonction p-n, générant un courant de dérive qui contrecarre le courant de diffusion.
Ce champ électrique s’oppose également à toute diffusion ultérieure de porteurs majoritaires à travers la jonction.
À l’équilibre, le courant total aux bornes de la jonction est de la même amplitude dans les deux sens et est indiqué par une énergie de Fermi constante.

bases des semi-conducteurs

P-N junction

Une jonction p-n est formée lorsque des matériaux semi-conducteurs de type p et de type n sont assemblés. À l'interface de la jonction p-n, les trous du côté p et les électrons du côté n commencent à diffuser dans les côtés opposés en raison du gradient de concentration. Cette diffusion de porteurs conduit à une région autour de la jonction où il n’y a pas de porteurs de charge libres, connue sous le nom de région d’appauvrissement. La densité de charge dans la région d'appauvrissement pour le côté n et le côté p peut être décrite par les équations:
<img alt="Equation 1" src="/files/ftp_upload/15156/15156_Equation_1.svg" style="height: 20px;">
Où q est la charge élémentaire, N_D et N_A sont respectivement les concentrations de dopage donneur et accepteur.
Les charges fixes dans la région d'appauvrissement créent un champ électrique (E), pointant du côté n vers le côté p, s'opposant à une diffusion ultérieure des porteurs. Ce champ électrique donne lieu à une différence de potentiel aux bornes de la jonction, connue sous le nom de tension intégrée (V_0), qui peut être calculée par:
<img alt="Equation 2" src="/files/ftp_upload/15156/15156_Equation_2v2.svg" style="height: 40px;">
Où V_T est la tension thermique et n_i est la concentration intrinsèque de porteurs.
Il existe deux types de courants dans une jonction p-n : le courant de diffusion dû à la diffusion des porteurs et le courant de dérive dû au champ électrique. À l'équilibre, l'amplitude du courant de diffusion est égale à l'amplitude du courant de dérive, ce qui entraîne l'absence de flux de courant net à travers la jonction. Dans des conditions de circuit ouvert, il n'y a pas de courant externe et la tension intégrée de la couche d'appauvrissement équilibre le potentiel de contact au niveau des jonctions métal-semi-conducteur, ce qui entraîne une tension nette nulle aux bornes.
La tension de barrière intégrée et la largeur de la région d'appauvrissement jouent un rôle essentiel dans le comportement de la jonction. La largeur de la région d'appauvrissement détermine la capacité de la jonction et affecte la façon dont la jonction répondra aux tensions externes.

Bases des semi-conducteurs

Les lampadaires solaires fonctionnent indépendamment sans avoir besoin d’une alimentation externe, car ils contiennent des jonctions p-n dans leurs cellules solaires.
Un...

Education

Enseignement

JoVE Core

Electrical Engineering

Génie électrique

Unit 1

Unité 1

Basics of Semiconductors

Les bases des semi-conducteurs

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 charges in this region create an electric field that points from the n-side to the p-side. That field opposes further carrier diffusion and helps set up the junction’s built-in voltage, V0.

The built-in voltage across the junction depends on the thermal voltage, VT, and the intrinsic carrier concentration, ni. A p-n junction also has two kinds of current: diffusion current from carrier movement and drift current from the electric field. At equilibrium, these currents are equal in magnitude, so there is no net current flow across the junction.

Under open-circuit conditions, no external current flows. The built-in voltage in the depletion layer balances the contact potential at the metal-semiconductor junctions, so the terminals show zero net voltage. The barrier voltage and the width of the depletion region are important because they control junction behavior and affect the capacitance and response to external voltages.

P-N Junction Depletion Region

energy bands in solids

Valence and Conduction Bands in Silicon

Valence and conduction bands explain how electrons behave in solids. In isolated atoms, electrons occupy discrete energy levels that the Bohr model describes well. The hydrogen atom, for example, has specific electron energies labeled by the quantum number n, and higher n values give levels that are less negative and closer together. When atoms move close together in a solid, those discrete levels start to split. This happens because electron orbitals from neighboring atoms overlap. The Pauli...

semiconductors

Energy Bands in Metals and Insulators

Materials conduct electricity in different ways because their energy bands are arranged differently. Metals, semiconductors, and insulators can be compared with energy band diagrams. These diagrams show how easily electrons can move when an electric field is applied. Metals such as copper, zinc, and lead have low resistivity. Their conduction band is not fully occupied, or it overlaps with the valence band, so a band gap is essentially absent. Electrons in the highest valence energy levels can...

types of semiconductors

Intrinsic and Doped Semiconductors

Intrinsic semiconductors are very pure materials with no impurities. At absolute zero, they act as perfect insulators because the valence electrons are bound and the conduction band is empty. That means electrical conduction cannot occur under those conditions. The Fermi level helps describe the chance that an energy level is occupied by an electron at thermal equilibrium. In an intrinsic semiconductor, the Fermi level sits near the middle of the band gap at absolute zero. As temperature...

carrier generation and recombination

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...

carrier transport

Drift and Diffusion in Semiconductors

Drift and diffusion are the two main ways electric current forms in semiconductors. These charge-carrier motions help determine how semiconductor devices work and how well they perform. The carriers involved are electrons and holes. Drift current begins when an external electric field acts on charge carriers. Electrons and holes move between collisions with lattice atoms, and this motion creates drift velocity. For electrons, drift velocity depends on electron mobility and the electric field...

p-n junction

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 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...

metal-semiconductor junctions

Schottky and Ohmic Metal Contacts

Metal contacts with semiconductors can form either Schottky or Ohmic junctions. The result depends on the work function of the metal, the work function of the semiconductor, and how electrons move when the two materials touch. At equilibrium, the Fermi levels align, so charge shifts until both sides match in energy. Schottky barriers form when a metal with work function Φm contacts a semiconductor with a different work function Φs. If Φm is greater than Φs, the semiconductor Fermi level starts...

biasing of metal-semiconductor junctions

How Bias Changes Metal-Semiconductor Current

Biasing metal-semiconductor junctions means applying a voltage across the junction. The metal connects to the voltage source, and the semiconductor is grounded. This setup helps control the direction and size of current in devices such as diodes, transistors, and photovoltaic cells. In a Schottky junction with an n-type semiconductor, a positive voltage on the metal lowers its Fermi level. A Fermi level is the energy level that helps describe how electrons are distributed. Lowering this level...

fermi level

Fermi Level in Semiconductors

The Fermi level is a key energy level in semiconductors. It sits between the lower-energy valence band and the higher-energy conduction band. The Fermi-Dirac function, which follows an S-shaped curve, shows the chance that an energy state is filled by an electron at a given temperature. At absolute zero, electrons occupy every energy state up to the Fermi level. States above it stay empty. As temperature rises, electrons gain energy and can move into vacant states above the Fermi level. In an...

fermi level dynamics

Vacuum Level and Schottky Barriers

Vacuum level and Schottky barriers help explain how electrons move between materials. The vacuum level is the energy needed for an electron to escape a material surface. In a semiconductor, it usually sits above the conduction band and serves as a reference for comparing electron energy. Electron affinity is the energy gap between the conduction band minimum and the vacuum level. It shows how easily a semiconductor can accept extra electrons. The work function is the least energy needed to...

key terms and concepts

Learn how a p-n junction creates a depletion region, built-in voltage, and balance between diffusion and drift currents in semiconductor devices.

P-N Junction Depletion Region | 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 Depletion Region

Description

Transcript

Tags