Name: how bias changes metal-semiconductor current
Uploaded: 2024-07-08T13:20:09.000Z
Duration: 1 min 27 s
Channel: JoVE

Beim Vorspannen von Metall- und n-Halbleiterübergängen wird eine Spannung an das Metall angelegt, während der Halbleiter geerdet wird. Der resultierende Strom ist positiv, wenn er vom Metall zum Halbleiter fließt.
Bei Schottky-Übergängen senkt das Anlegen einer positiven Spannung den Fermi-Spiegel des Metalls, wodurch die Barriere für Elektronen im Halbleiter verringert und der Netto-Elektronenfluss vom Halbleiter zum Metall ermöglicht wird. Dies führt zu einem schnell ansteigenden Vorwärtsvorspannungsstrom.
Umgekehrt erhöht eine negative Spannung den Fermi-Spiegel der Metalle und blockiert den Elektronenfluss vom Halbleiter zum Metall. Einige Elektronen überwinden jedoch die Sperrschichtbarriere, was zu einem kleinen Sperrstrom führt.
Bei ohmschen Übergängen löst bereits eine kleine positive Spannung einen großen Durchlassstrom aus, da keine Barriere vorhanden ist. Bei der Sperrvorspannung existiert eine kleine Barriere für den Elektronenfluss vom Metall zum Halbleiter, die verschwindet, wenn die Sperrvorspannung einige Zehntel Volt überschreitet.
Bei Kontakten, die mit Metall- und p-Halbleitern gebildet wurden, ist das Verhalten umgekehrt.
Die Vorspannung von Metall-Halbleiter-Kontakten ermöglicht die Kontrolle des Stromflusses, die in Geräten wie Dioden, Transistoren und Photovoltaikzellen unerlässlich ist.

vorspannung von metall-halbleiter-Übergängen

Bei der Vorspannung von Metall-Halbleiter-Übergängen wird eine Spannung über den Übergang angelegt. Genauer gesagt wird das Metall an eine Spannungsquelle angeschlossen, während der Halbleiter geerdet ist. Diese Technik ist wichtig, um die Richtung und Stärke des Stromflusses in elektronischen Geräten wie Dioden, Transistoren und Photovoltaikzellen zu steuern.

Bei Schottky-Übergängen, bei denen der Halbleiter vom Typ n ist, verringert das Anlegen einer positiven Spannung an das Metall im Verhältnis zum Halbleiter dessen Fermi-Niveau. Dadurch wird die Energiebarriere gesenkt, die die Elektronen im Halbleiter überwinden müssen, um in das Metall zu gelangen. Dies ermöglicht einen erheblichen Elektronenfluss vom Halbleiter zum Metall, was zu einem schnell ansteigenden Strom führt, wenn der Übergang in Vorwärtsrichtung vorgespannt ist. Wenn eine negative Spannung angelegt wird, kehrt sich die Situation um. Das Fermi-Niveau des Metalls steigt an und erhöht die Barriere gegen den Elektronenfluss vom Halbleiter zum Metall. Einige Elektronen können die Barriere trotzdem überwinden und einen geringen Sperrstrom erzeugen.

Ohmsche Übergänge verhalten sich anders. Da keine nennenswerte Barriere vorhanden ist, kann selbst eine geringe positive Spannung einen großen Vorwärtsstrom induzieren, der einen leichten Elektronenfluss vom Halbleiter zum Metall ermöglicht. Bei Sperrspannung gibt es eine minimale Barriere für den Elektronenfluss vom Metall zum Halbleiter, aber diese Barriere verschwindet praktisch, wenn die Sperrspannung einige Zehntel Volt überschreitet.

Die Wechselwirkungsdynamik ändert sich bei p-Typ-Halbleitern. Das für n-Typ-Halbleiter beschriebene Verhalten in Schottky- und Ohmschen Übergängen ist umgekehrt. Diese Fähigkeit, den Stromfluss durch Vorspannung zu manipulieren, ist für den Betrieb vieler elektronischer Komponenten von entscheidender Bedeutung und bildet die Grundlage für die Funktionalität einer breiten Palette von Geräten.

Vorspannung von Metall-Halbleiter-Übergängen

Beim Vorspannen von Metall- und n-Halbleiterübergängen wird eine Spannung an das Metall angelegt, während der Halbleiter geerdet wird. Der resultierende Strom ist positiv ...

Education

Lehre

JoVE Core

Electrical Engineering

Elektrotechnik

Unit 1

Einheit 1

Basics of Semiconductors

Grundlagen der Halbleiter

KEY TERMS AND CONCEPTS

ZENTRALE BEGRIFFE UND KONZEPTE

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 reduces the barrier electrons in the semiconductor must cross to move into the metal. As a result, many electrons flow from the semiconductor to the metal, and the current rises quickly in forward bias.

A negative voltage reverses this effect. The metal Fermi level rises, which increases the barrier for electrons moving from the semiconductor to the metal. A small reverse current can still appear because a few electrons are able to cross the barrier.

Ohmic junctions behave differently because they do not have a large barrier. Even a small positive voltage can produce a large forward current, so electrons move easily from the semiconductor to the metal. In reverse bias, there is only a small barrier for electrons moving from the metal to the semiconductor, and that barrier can disappear if the reverse voltage goes beyond a few tenths of a volt.

The behavior changes again with p-type semiconductors. In both Schottky and Ohmic junctions, the n-type behavior is reversed. This control over current flow is important for many electronic components and supports the function of a wide range of devices.

How Bias Changes Metal-Semiconductor Current

how-bias-changes-metal-semiconductor-current

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

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 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

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 biasing changes current in Schottky and Ohmic metal-semiconductor junctions, including n-type and p-type behavior in electronics.

How Bias Changes Metal-Semiconductor Current | 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

How Bias Changes Metal-Semiconductor Current

Description

Transcript

Tags