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

I lampioni solari funzionano in modo indipendente senza la necessità di un'alimentazione esterna, poiché contengono giunzioni PN all'interno delle loro celle solari.
Una giunzione p-n si forma aggiungendo impurità pentavalenti a un sottile foglio di silicio di tipo p, convertendo parte di esso in silicio di tipo n.
Il gradiente di concentrazione dei portatori di carica su entrambi i lati della lamina di silicio porta alla diffusione di lacune dal lato p al lato n e di elettroni dal lato n al lato p, generando una corrente di diffusione.
La regione vicino all'incrocio diventa priva di vettori di carica gratuiti, formando la regione di esaurimento. Inoltre, le cariche positive e negative nette rimangono in questa regione, creando un campo elettrico e una differenza di potenziale attraverso la giunzione.
Il campo elettrico sposta i portatori di minoranza nella giunzione p-n, generando una corrente di deriva che contrasta la corrente di diffusione.
Questo campo elettrico si oppone anche a qualsiasi ulteriore diffusione di portatori di maggioranza attraverso l'incrocio.
All'equilibrio, la corrente totale attraverso la giunzione è la stessa in grandezza in entrambe le direzioni ed è indicata dall'energia di Fermi costante.

nozioni di base sui semiconduttori

P-N junction

Una giunzione p-n, si forma quando i materiali semiconduttori di tipo p e di tipo n vengono uniti insieme. All'interfaccia della giunzione p-n, le lacune del lato p e gli elettroni del lato n iniziano a diffondersi nei lati opposti a causa del gradiente di concentrazione. Questa diffusione di portatori porta ad una regione attorno alla giunzione dove non ci sono portatori di carica liberi, nota come regione di svuotamento. La densità di carica all'interno della regione di svuotamento per il lato n e il lato p può essere descritta dalle equazioni:

<img alt="Equation 1" src="/files/ftp_upload/15156/15156_Equation_1.svg" style="height: 20px;">

Dove q è la carica elementare, ND e NA sono rispettivamente le concentrazioni di drogaggio del donatore e dell’accettore.

Le cariche fisse nella regione di svuotamento creano un campo elettrico (E), che punta dal lato n al lato p, opponendosi all'ulteriore diffusione dei portatori. Questo campo elettrico dà origine ad una differenza di potenziale ai capi della giunzione, nota come tensione incorporata (V0), che può essere calcolata come:

<img alt="Equation 2" src="/files/ftp_upload/15156/15156_Equation_2v2.svg" style="height: 40px;">

Dove VT è la tensione termica e ni è la concentrazione intrinseca del portatore.

Esistono due tipi di correnti in una giunzione p-n: la corrente di diffusione dovuta alla diffusione del portatore e la corrente di deriva dovuta al campo elettrico. All'equilibrio, l'entità della corrente di diffusione è uguale all'entità della corrente di deriva, portando flusso di corrente netto attraverso la giunzione pari a zero. In condizioni di circuito aperto, non c'è corrente esterna e la tensione incorporata nello strato di svuotamento, bilancia il potenziale di contatto sulle giunzioni metallo-semiconduttore, risultando in una tensione netta pari a zero tra i terminali.

La tensione di barriera incorporata e l'ampiezza della regione di svuotamento svolgono un ruolo critico nel comportamento della giunzione. La larghezza della regione di svuotamento determina la capacità della giunzione e influenza il modo in cui la giunzione risponderà alle tensioni esterne.

Nozioni di Base sui Semiconduttori

I lampioni solari funzionano in modo indipendente senza la necessità di un'alimentazione esterna, poiché contengono giunzioni PN all'interno delle loro celle solari.
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Electrical Engineering

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Basics of Semiconductors

Fondamenti dei semiconduttori

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TERMINI E CONCETTI CHIAVE

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

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