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

ソーラー街路灯は、太陽電池内にpn接合が含まれているため、外部電源を必要とせずに独立して機能します。
p-n接合は、薄いp型シリコンシートに五価不純物を添加し、その一部をn型シリコンに変換することによって形成されます。
シリコンシートの両側にある電荷キャリアの濃度勾配は、p側からn側への正孔とn側からp側への電子の拡散につながり、拡散電流を生成します。
接合部付近の領域には自由電荷担体がなくなり、空乏領域が形成されます。また、この領域には正味の正電荷と負電荷が残り、接合部全体に電界と電位差が生じます。
電界はpn接合の少数キャリアをドリフトさせ、拡散電流を打ち消すドリフト電流を生成します。
この電界は、接合部を横切る多数派キャリアのさらなる拡散にも反対します。
平衡状態では、接合部を横切る全電流は両方向で同じ大きさであり、一定のフェルミエネルギーによって示されます。

半導体の基礎

P-N junction

p-n 接合は、p 型と n 型の半導体材料が結合されたときに形成されます。p-n 接合の界面では、濃度勾配により、p 側からの正孔と n 側からの電子が反対側に拡散し始めます。このキャリアの拡散により、接合の周囲に自由電荷キャリアが存在しない領域 (空乏領域) が発生します。この領域は空乏領域と呼ばれます。n 側と p 側の空乏領域内の電荷密度は、次の式で表すことができます。

<img alt="Equation 1" src="/files/ftp_upload/15156/15156_Equation_1.svg" style="height: 20px;">

q は基本電荷、N_D と N_A はそれぞれドナーとアクセプタのドーピング濃度です。
空乏領域の固定電荷は、n 側から p 側に向かう電界 (E) を作成し、キャリアのさらなる拡散を阻止します。この電界により、接合部全体に電位差が生じます。これは内蔵電圧 (V_0) と呼ばれ、次のように計算できます。
<img alt="Equation 2" src="/files/ftp_upload/15156/15156_Equation_2v2.svg" style="height: 40px;">
ここで、V_T は熱電圧、n_i は固有キャリア濃度です。

p-n 接合部には、キャリア拡散による拡散電流と電界によるドリフト電流の 2 種類の電流が存在します。平衡状態では、拡散電流の大きさはドリフト電流の大きさに等しく、接合部を流れる正味電流はありません。開回路状態では、外部電流はなく、空乏層の内蔵電圧が金属半導体接合部の接触電位とバランスを取り、端子間の正味電圧はゼロになります。
ビルトインバリア電圧と空乏領域の幅は、接合部の動作に重要な役割を果たします。空乏領域の幅によって接合部の静電容量が決まり、接合部が外部電圧にどのように反応するかに影響します。

ソーラー街路灯は、太陽電池内にpn接合が含まれているため、外部電源を必要とせずに独立して機能します。
ある。。。

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

Basics of Semiconductors

KEY TERMS AND CONCEPTS

主要用語と概念

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 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 Depletion Region

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