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

태양광 가로등은 태양 전지 내에 pn 접합을 포함하고 있기 때문에 외부 전원 공급 장치 없이 독립적으로 작동합니다.
p-n 접합은 얇은 p형 실리콘 시트에 5가 불순물을 첨가하여 그 일부를 n형 실리콘으로 변환하여 형성됩니다.
실리콘 시트의 양쪽에 있는 전하 캐리어의 농도 구배는 p측에서 n측으로 정공을 확산시키고 n측에서 p측으로 전자를 확산시켜 확산 전류를 생성합니다.
접합부 근처의 영역에는 자유 전하 캐리어가 없어 공핍 영역이 형성됩니다. 또한 순 결합 양전하와 음전하가 이 영역에 남아 접합부에 전기장과 전위차를 생성합니다.
전기장은 p-n 접합에서 소수 캐리어를 드리프트하여 확산 전류를 상쇄하는 드리프트 전류를 생성합니다.
이 전기장은 또한 접합부를 가로지르는 대다수 캐리어의 추가 확산에 반대합니다.
평형 상태에서 접합부를 가로지르는 총 전류는 양방향에서 크기가 동일하며 일정한 페르미 에너지로 표시됩니다.

반도체의 기초

P-N junction

p형 반도체와 n형 반도체 물질이 서로 접합되면 p-n 접합이 형성됩니다. p-n 접합의 경계면에서는 농도 구배로 인해 p 측의 정공과 n 측의 전자가 반대쪽으로 확산되기 시작합니다. 캐리어의 이러한 확산은 공핍 영역으로 알려진 자유 전하 캐리어가 없는 접합 주변 영역으로 이어집니다. n측과 p측에 대한 공핍 영역 내의 전하 밀도는 다음 방정식으로 설명할 수 있습니다.

<img alt="Equation 1" src="/files/ftp_upload/15156/15156_Equation_1.svg" style="height: 20px;">

q가 기본 전하인 경우 N_D와 N_A는 각각 도너 및 수용체 도핑 농도입니다.

공핍 영역의 고정 전하는 n측에서 p측을 가리키는 전기장(E)을 생성하여 캐리어의 추가 확산을 방해합니다. 이 전기장은 접합부 전체에 내장 전압(V_0)으로 알려진 전위차를 발생시킵니다. 이는 다음과 같이 계산할 수 있습니다.

<img alt="Equation 2" src="/files/ftp_upload/15156/15156_Equation_2v2.svg" style="height: 40px;">

 여기서 V_T는 열 전압이고 n_i는 고유 캐리어 농도입니다.

pn 접합에 존재하는 전류에는 캐리어 확산으로 인한 확산 전류와 전계로 인한 표동전류의 두 가지 유형이 있습니다. 평형 상태에서 확산 전류의 크기는 표동전류의 크기와 동일하므로 접합을 통과하는 순 전류 흐름이 발생하지 않습니다. 개방 회로 조건에서는 외부 전류가 없으며 공핍층에 내장된 전압이 금속 반도체 접합에서 접촉 전위의 균형을 유지하여 단자 전체의 순 전압이 0이 됩니다.

내장된 장벽 전압과 공핍 영역의 폭은 접합의 동작에 중요한 역할을 합니다. 공핍 영역의 폭은 접합의 정기용량을 결정하고 접합이 외부 전압에 반응하는 방식에 영향을 줍니다.

태양광 가로등은 태양 전지 내에 pn 접합을 포함하고 있기 때문에 외부 전원 공급 장치 없이 독립적으로 작동합니다.
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Education

교육

JoVE Core

Electrical Engineering

전기공학

Unit 1

제1단원

Basics of Semiconductors

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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

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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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