Name: p-n junction diode under bias
Uploaded: 2025-05-22T09:06:15.000Z
Duration: 1 min 16 s
Channel: JoVE

LED内のpn接合は、光を生成するために外部バイアスを必要とします。
フォワードバイアスでは、pn接合に電圧を印加し、バッテリの正端子をp側に、負端子をn側に接続します。印加電圧は接合電位に対抗するため、バリア幅が狭くなります。
このバリア幅の縮小により、マジョリティキャリアの拡散を増加させることで電流を流すことができます。拡散電流はドリフト電流よりも高く、正味電流はpからnに順方向に流れます。
拡散時には、接合領域の電子と正孔の再結合により光子が放出され、LEDが光ります。
逆バイアスでは、バッテリのプラス端子はn側に接続され、マイナス端子はp側に接続されます。
これにより、印加された電位が接合電位に加わるため、LEDが光るのを防ぎ、バリア幅が拡大し、過半数キャリア拡散が減少します。
正味電流は、少数キャリアによって得られる小さなドリフト電流です。
逆バイアス電圧が一定の閾値を超えると、ジャンクションブレークダウンが発生し、大電流が流れます。

pn接合のバイアス

pn接合ダイオードの動作には、順バイアス、逆バイアス、および平衡などのさまざまなバイアス条件が含まれます。

平衡状態では、pn接合に外部電圧がかかっていません。キャリアの拡散により接合界面に空乏層が形成され、p側にはアクセプター、n側にはドナーの帯電したドーパントが残ります。これらの不動電荷はキャリアのさらなる拡散を防ぐ電場を作り出します。関連するエネルギーバンド図は、両側のフェルミ準位が一致していることを示しており、これは平衡を示しています。接合全体にかかる内蔵電位は、接合を横切るキャリアの正味の流れを防ぎます。
順方向バイアスでは、印加された電圧が障壁電位を減少させ、空乏層の幅を狭めます。その結果、キャリアは容易に接合を横切ることができ、対応するバンド図はエネルギーバンドが上向きに曲がり、障壁電位の減少を示します。順方向バイアス下でのダイオードを横切る電流は、印加電圧に対して指数関数的に増加します。
逆方向バイアスでは、外部電圧が逆方向に印加され、空乏層が広がり、障壁電位が増加し、キャリアが接合を横切るのが難しくなり、電流の流れが非常に小さな逆方向飽和電流に減少します。逆方向バイアスのエネルギーバンド図は、バンドが下向きに曲がり、障壁電位が増加していることを示します。逆方向バイアスの電流は小さな一定値で、飽和電流に近いですが符号が反対であり、空乏層内の熱生成によるキャリアのわずかな流れを反映しています。

LED内のpn接合は、光を生成するために外部バイアスを必要とします。
フォワードバイアスでは、pn接合に電圧を印加します...

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 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 in balance. A built-in potential also exists across the junction. This potential prevents a net flow of carriers from one side to the other.

When the diode is forward biased, the applied voltage lowers the barrier potential. It also narrows the depletion region. Carriers can then cross the junction more easily. The band diagram shows the energy bands bending upward, which matches the reduced barrier.

Forward bias also causes the current to rise quickly as the applied voltage increases. The current increases exponentially with voltage. In reverse bias, the external voltage is applied in the opposite direction. The depletion region widens, the barrier potential increases, and carrier flow becomes very small.

The reverse-bias band diagram shows the energy bands bending downward. This change reflects the higher barrier potential. The current falls to a small reverse saturation current. It stays close to that saturation value and has the opposite sign, because only a minor carrier flow remains from thermal generation within the depletion region.

P-N Junction Diode Under Bias

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 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

Explore equilibrium, forward bias, and reverse bias in a p-n junction diode, including depletion region changes, band diagrams, and current flow.

P-N Junction Diode Under Bias | 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

P-N Junction Diode Under Bias

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