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

金属とn型半導体接合のバイアスには、半導体を接地しながら金属に電圧を印加することが含まれます。結果として生じる電流は、金属から半導体に流れるときに正になります。
ショットキー接合の場合、正の電圧を印加すると金属のフェルミ準位が低下し、半導体内の電子の障壁が減少し、半導体から金属への正味の電子の流れが可能になります。これにより、順方向バイアス電流が急速に増加します。
逆に、負の電圧は金属のフェルミ準位を上昇させ、半導体から金属への電子の流れを遮断します。ただし、一部の電子は接合障壁を乗り越えるため、逆バイアス電流が小さくなります。
オーミック接合の場合、小さな正電圧でも、バリアがないために大きな順方向バイアス電流が引き起こされます。逆バイアスでは、金属から半導体への電子の流れに小さな障壁が存在し、逆バイアスが数十分の1ボルトを超えると、これは消えます。
金属やp型半導体で形成された接点では、動作が逆になります。
金属-半導体接合をバイアスすることで、ダイオード、トランジスタ、太陽電池などのデバイスに不可欠な電流の流れを制御することができます。

金属半導体接合のバイアス

金属半導体接合のバイアスには、接合全体に電圧をかけることが含まれます。具体的には、金属は電圧源に接続され、半導体は接地されます。この技術は、ダイオード、トランジスタ、光電池などの電子デバイスにおける電流の方向と大きさを制御するために不可欠です。

半導体が n 型であるショットキー接合では、半導体に対して金属に正の電圧をかけると、フェルミ準位が低下します。これにより、半導体内の電子が金属に移動するために克服する必要があるエネルギー障壁が低下します。これにより、半導体から金属への電子の大きな流れが可能になり、接合が順バイアスされているときに電流が急速に増加します。負の電圧が適用される場合、状況は逆転します。金属のフェルミ準位が上昇し、半導体から金属への電子の流れに対する障壁が強化されます。これにもかかわらず、いくつかの電子が障壁を乗り越えることができ、わずかな逆バイアス電流が生成されます。
オーミック接合は異なる動作をします。大きな障壁がないため、わずかな正電圧でも大きな順方向バイアス電流を誘導し、半導体から金属への電子の流れを容易にします。逆バイアスでは、金属から半導体への電子の流れに対する最小限の障壁が存在しますが、逆バイアス電圧が数十分の1ボルトを超えると、この障壁は事実上消滅します。
p型半導体では相互作用のダイナミクスが変わります。ショットキー接合とオーミック接合の両方でn型半導体について説明されている動作は逆になります。バイアスによって電流の流れを操作するこの能力は、多くの電子部品の動作に不可欠であり、幅広いデバイスの機能の基盤となります。

金属とn型半導体接合のバイアスには、半導体を接地しながら金属に電圧を印加することが含まれます。結果として生じる電流は正です...

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

Basics of Semiconductors

半導体の基礎

KEY TERMS AND CONCEPTS

主要用語と概念

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 電気工学 は、電気回路の基本概念と回路解析テクニックを網羅したアニメーションビデオシリーズです。オペアンプと回路変換および 1 次・ 2 次回路の概念を網羅しています。実験を撮影した実写動画では、設計例や現代社会での応用が含まれており、複雑な概念も分かりやすく学習いただけます。

electrical engineering

How Bias Changes Metal-Semiconductor Current

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