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

Solarne latarnie uliczne działają niezależnie, bez konieczności korzystania z zewnętrznego źródła zasilania, ponieważ zawierają złącza p-n w swoich ogniwach słonecznych.
Złącze p-n jest tworzone przez dodanie pięciowartościowych zanieczyszczeń do cienkiego arkusza krzemu typu p, przekształcając jego część w krzem typu n.
Gradient stężeń nośników ładunku po obu stronach arkusza krzemu prowadzi do dyfuzji ze strony p na stronę n i elektronów ze strony n na stronę p, generując prąd dyfuzyjny.
Obszar w pobliżu skrzyżowania staje się pozbawiony nośników bezpłatnych ładunków, tworząc obszar zubożenia. Ponadto w tym regionie pozostają ładunki dodatnie i ujemne związane z netto, tworząc pole elektryczne i różnicę potencjałów na złączu.
Pole elektryczne dryfuje mniejszościowe nośniki w złączu p-n, generując prąd dryfujący, który przeciwdziała prądowi dyfuzyjnemu.
To pole elektryczne sprzeciwia się również dalszemu dyfuzji nośników większościowych w poprzek skrzyżowania.
W stanie równowagi całkowity prąd przepływający przez złącze ma taką samą wielkość w obu kierunkach i jest wskazywany przez stałą energię Fermiego.

podstawy półprzewodników

P-N junction

Złącze p-n powstaje w wyniku połączenia materiałów półprzewodnikowych typu p i n. Na styku złącza p-n dziury od strony p i elektrony od strony n zaczynają dyfundować w przeciwne strony ze względu na gradient stężeń. Ta dyfuzja nośników prowadzi do obszaru wokół złącza, w którym nie ma wolnych nośników ładunku, zwanego obszarem wyczerpania. Gęstość ładunku w obszarze wyczerpania dla strony n i p można opisać równaniami:

<img alt="Equation 1" src="/files/ftp_upload/15156/15156_Equation_1.svg" style="height: 20px;">

Gdzie q to ładunek elementarny, N_D i N_A to odpowiednio stężenia domieszki donora i akceptora.

Stałe ładunki w obszarze zubożenia tworzą pole elektryczne (E), skierowane od strony n do strony p, przeciwstawiając się dalszej dyfuzji nośników. To pole elektryczne powoduje powstanie różnicy potencjałów na złączu, zwanej napięciem wbudowanym (V_0), którą można obliczyć ze wzoru:

<img alt="Equation 2" src="/files/ftp_upload/15156/15156_Equation_2v2.svg" style="height: 40px;">

Gdzie, V_T to napięcie termiczne, a ni to wewnętrzne stężenie nośnika.

W złączu p-n występują dwa rodzaje prądów: prąd dyfuzyjny spowodowany dyfuzją nośnika i prąd dryfowy powodowany polem elektrycznym. W stanie równowagi wielkość prądu dyfuzyjnego jest równa wielkości prądu dryfu, co prowadzi do braku przepływu prądu netto przez złącze. W warunkach obwodu otwartego nie ma prądu zewnętrznego, a napięcie wbudowane w warstwę zubożoną równoważy potencjał stykowy na złączach metal-półprzewodnik, co skutkuje zerowym napięciem sieciowym na zaciskach.

Wbudowane napięcie barierowe i szerokość obszaru zubożenia odgrywają kluczową rolę w zachowaniu złącza. Szerokość obszaru zubożenia określa pojemność złącza i wpływa na to, jak złącze będzie reagować na napięcia zewnętrzne.

Podstawy półprzewodników

Solarne latarnie uliczne działają niezależnie, bez konieczności korzystania z zewnętrznego źródła zasilania, ponieważ zawierają złącza p-n w swoich ogniwach słonecznych.
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Education

JoVE Core

Electrical Engineering

Elektrotechnika

Unit 1

Jednostka 1

Basics of Semiconductors

KEY TERMS AND CONCEPTS

KLUCZOWE TERMINY I POJĘCIA

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

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semiconductors

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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

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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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