Name: valence and conduction bands in silicon
Uploaded: 2024-07-08T13:20:08.000Z
Duration: 1 min 1 s
Channel: JoVE

고체는 뚜렷한 전자 구성과 에너지 준위를 가진 원자로 구성됩니다.
두 개의 동일한 고립 된 원자가 서로 가까워지면 상호 작용으로 인해 각 에너지 준위가 두 개의 별개의 수준으로 나뉩니다.
이 분할은 원자의 두 전자가 동시에 동일한 에너지 상태를 차지할 수 없다는 Pauli 배제 원리의 결과입니다.
여러 원자가 모여 고체를 형성하면 에너지 준위가 분리되어 연속적인 띠를 형성합니다. 평형 원자간 간격에서 띠는 원자가 띠와 전도대로 나뉩니다.
절대 영도 온도에서 원자가 밴드는 전자로 채워진 에너지 준위로 구성됩니다.
원자가 밴드 위에는 빈 에너지 준위를 포함하는 전도대가 있습니다.
이 두 밴드 사이의 에너지 갭을 밴드 갭이라고 합니다. 원자가 대역의 상단과 전도대의 하단 사이의 에너지 차이를 나타냅니다.

반도체의 기초

Energy Bands in Solids

고립된 원자는 보어 모델로 잘 설명되는 이산 에너지 준위를 가지고 있습니다. 그리고, 수소 원자에 있는 전자의 에너지를 E_n으로 정량화합니다. 양자수 'n'이 높을수록 음수가 적고 전자 에너지 준위가 더 가까워집니다.
 띠 형성:
원자가 고체처럼 서로 가까워지면 인접한 원자의 전자 궤도가 겹쳐서 이러한 개별 에너지 준위가 분리되기 시작합니다. 이러한 분할은 두 개의 전자가 동시에 동일한 양자 상태를 차지할 수 없다는 Pauli 배제 원리로 인해 발생합니다. 더 많은 원자가 결합할수록 불연속적인 에너지 준위의 수가 증가하고, 분할이 너무 미세해져서 연속적인 에너지 띠를 형성합니다. 평형 원자간 거리로 알려진 특정 지점에서 이들 띠는 전자로 채워진 원자가 띠와 절대 영도 온도에서 비어 있는 전도 띠가 됩니다.
반도체의 에너지 띠:
에너지 띠 구조는 14개의 전자를 갖는 실리콘과 같은 반도체에서 더 복잡합니다. 내부 10개의 전자는 깊은 에너지 준위를 차지하며 결합에 기여하지 않습니다. 3s 및 3p 하위 껍질에 있는 나머지 4개의 원자가 전자는 재료의 화학적, 전기적 특성을 결정합니다. 실리콘 원자가 결정 격자를 형성함에 따라 3s 및 3p 하위 껍질이 겹쳐서 띠를 형성합니다. 결정의 평형 거리에서 이러한 띠는 원자가 띠에 대해 4N 상태를 포함하고 전도 띠에 대해 4N 상태를 포함합니다. 여기서 N은 실리콘 원자의 수입니다.
띠틈 크기는 전자가 전도대로 얼마나 쉽게 여기될 수 있는지를 결정하기 때문에 중요합니다. 이 띠틈은 열 에너지나 빛이 틈을 가로질러 전자를 여기시켜 전기 전도를 일으킬 수 있을 정도로 반도체에 충분히 작습니다.

고체는 뚜렷한 전자 구성과 에너지 준위를 가진 원자로 구성됩니다.
두 개의 동일한 고립 된 원자가 서로 가까워지면 ...

Education

교육

JoVE Core

Electrical Engineering

전기공학

Unit 1

제1단원

Basics of Semiconductors

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 exclusion principle also applies, since no two electrons can share the same quantum state. As more atoms are added, the splitting becomes so small that it appears as a continuous energy band.

At the equilibrium interatomic distance, these bands form the valence band and the conduction band. The valence band is filled with electrons at this point. The conduction band is empty at absolute zero temperature. This separation helps explain why some solids conduct electricity and others do not.

Silicon shows how band formation works in a semiconductor. A silicon atom has 14 electrons, but the inner 10 electrons stay in deep energy levels and do not take part in bonding. The remaining four valence electrons, which occupy the 3s and 3p subshells, control the material’s chemical and electrical behavior. As silicon atoms arrange into a crystal lattice, the 3s and 3p subshells overlap and form bands.

In the crystal, the valence band and conduction band each contain 4N states, where N is the number of silicon atoms. The bandgap, or energy gap between the bands, is important because it controls how easily electrons can move into the conduction band. In semiconductors, this gap is small enough that thermal energy or light can excite electrons across it, which allows electrical conduction.

Valence and Conduction Bands in Silicon

energy bands in solids

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

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 atomic energy levels split into valence and conduction bands, and why silicon’s small bandgap lets heat or light drive conduction.

Valence and Conduction Bands in Silicon | 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

Valence and Conduction Bands in Silicon

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