Band Gap and Semiconductor Current Carriers | Intermediate Electronics
Summary
TLDRThis video explains the concept of band gap and current carriers in semiconductors. It covers the structure of atoms, the energy levels of electrons, and the difference between the valence and conduction bands. The video explores how the band gap affects the conductivity of materials like insulators, semiconductors, and conductors. It also introduces free electrons and holes as the two types of current carriers in semiconductors and explains how they contribute to electron and hole currents. Viewers gain a fundamental understanding of how current is produced in semiconductor materials.
Takeaways
- 🔬 Band gap is the energy difference between the valence band and conduction band, determining how easily electrons can move.
- ⚛️ In the Bohr model, atoms consist of neutrons, protons, and electrons, with valence electrons in the outermost shell, called the valence band.
- ⚡ Electrons in the valence band can gain enough energy to jump to the conduction band, enabling current flow in semiconductors.
- 🚫 Insulators have a large band gap, preventing easy electron movement, which results in poor conductivity.
- 🟢 Semiconductors have a smaller band gap, allowing electrons to move into the conduction band when external energy is applied.
- ⚡ Conductors, like copper, have no band gap, allowing electrons to move freely and conduct electricity easily.
- 🛠️ In semiconductors, current is carried by both free electrons in the conduction band and holes in the valence band.
- 🌡️ At room temperature, some electrons in intrinsic silicon gain enough energy to jump into the conduction band, creating free electrons and holes.
- 🔋 Electron current is produced when free electrons move toward the positive end of a voltage source in the conduction band.
- 🔄 Hole current occurs in the valence band as electrons move into nearby holes, creating current without overlapping with electron current.
Q & A
What are the fundamental components of an atom according to the Bohr model?
-According to the Bohr model, an atom consists of a central nucleus containing protons and neutrons, with electrons orbiting around the nucleus in specific energy levels or shells.
What is the valence band in an atom?
-The valence band refers to the outermost shell of an atom, where the valence electrons are located. It represents a band of energy levels that the electrons are confined to.
How does an electron move from the valence band to the conduction band?
-An electron moves from the valence band to the conduction band when it gains sufficient energy from an external source to overcome the band gap, allowing it to escape the valence band.
What is the 'band gap' in a semiconductor?
-The band gap is the difference in energy between the valence band and the conduction band. It is the amount of energy an electron needs to jump from the valence band to the conduction band.
Why do materials with a large band gap have poor conductivity?
-Materials with a large band gap have poor conductivity because the electrons in the valence band require a large amount of energy to jump to the conduction band, making it difficult for current to flow.
How does the band gap affect the conductivity of insulators, semiconductors, and conductors?
-In insulators, the band gap is very large, preventing electron movement and resulting in poor conductivity. In semiconductors, the band gap is smaller, allowing electrons to move to the conduction band with external energy. In conductors, the conduction and valence bands overlap, allowing free movement of electrons and excellent conductivity.
What are the two types of current carriers in a semiconductor?
-The two types of current carriers in a semiconductor are free electrons (which move in the conduction band) and holes (which represent the absence of an electron in the valence band).
How is electron current produced in a semiconductor?
-Electron current is produced when free electrons in the conduction band are attracted to the positive terminal of a voltage source, moving through the material and generating a flow of current.
What is hole current and how is it different from electron current?
-Hole current occurs in the valence band when electrons move into nearby holes, creating a flow of current. Unlike electron current, which happens in the conduction band, hole current is the result of electron movement within the valence band.
How do external factors, such as temperature or voltage, affect the generation of current in semiconductors?
-External factors like temperature or voltage can provide the energy needed for electrons to jump from the valence band to the conduction band, increasing the number of free electrons and holes, which in turn increases the current flow in semiconductors.
Outlines
🔍 Introduction to Band Gap and Semiconductor Current Carriers
This paragraph introduces the topics of band gap and current carriers in semiconductors. It begins by recalling basic chemistry concepts about atoms, including protons, neutrons, and electrons. The Bohr model is used to explain the structure of an atom with energy levels, or shells, surrounding the nucleus. The valence shell, also referred to as the valence band, contains electrons that can gain enough energy to escape to the conduction band, which is crucial for understanding how current is produced in semiconductors.
💡 Understanding Band Gap
Here, the concept of band gap is defined as the energy difference between the valence band and the conduction band. This energy must be supplied to a valence electron for it to jump to the conduction band, where it can move freely. The size of the band gap determines a material's conductivity. If the gap is large, the material has poor conductivity because electrons cannot easily reach the conduction band.
📊 Examining Energy Diagrams and Conductivity of Materials
The paragraph dives into energy diagrams of different materials—insulators, semiconductors, and conductors—and explains their conductivity based on the size of the band gap. Insulators have a large band gap, making it difficult for electrons to move. Semiconductors have a smaller band gap, allowing electrons to jump into the conduction band when provided with external energy. Conductors, like metals, have overlapping valence and conduction bands, which allows electrons to move freely and conduct electricity.
⚡ Current Carriers in Semiconductors
This paragraph introduces two main types of current carriers in semiconductors: free electrons and holes. It explains how atoms form solid crystalline materials through covalent bonding, and the example of silicon is used to illustrate how an intrinsic silicon crystal is formed. The text describes how valence electrons can jump into the conduction band, leaving behind holes in the valence band, both of which contribute to current generation in a semiconductor.
🌀 Electron Current in Semiconductors
Here, electron current is explained. At room temperature, intrinsic silicon crystals gain enough energy for some valence electrons to jump into the conduction band, creating free electrons. When a voltage is applied, these free electrons move toward the positive terminal of the voltage source, producing current in the material. This type of current is known as electron current.
🔄 Hole Current in Semiconductors
This section focuses on hole current, which occurs in the valence band. As valence electrons jump into the conduction band, vacancies, or holes, are left behind in the valence band. Electrons in the valence band can move into nearby holes, creating movement that generates a current known as hole current. Despite being caused by electron movement, it’s referred to as hole current to distinguish it from electron current in the conduction band.
📚 Conclusion and Recap of Band Gap and Semiconductor Current Carriers
The video concludes by summarizing the key topics covered: band gap, current carriers in semiconductors, and the energy diagrams of different materials (insulators, semiconductors, and conductors). The role of free electrons and holes in producing current in semiconductors is briefly revisited, and viewers are encouraged to ask questions or subscribe for more content.
Mindmap
Keywords
💡Band Gap
💡Semiconductor Current Carriers
💡Valence Band
💡Conduction Band
💡Energy Levels
💡Electron
💡Hole
💡Covalent Bonding
💡Intrinsic Silicon Crystal
💡Energy Diagram
💡External Energy
Highlights
Introduction to band gap and semiconductor current carriers to understand how current is produced in a semiconductor.
Atoms consist of neutrons, protons, and electrons, with the exception of normal hydrogen atoms which lack neutrons.
The Bohr model describes atoms as having a nucleus of protons and neutrons, surrounded by orbiting electrons.
Energy levels surrounding the nucleus are grouped into shells, and the outermost shell is called the valence shell.
Valence electrons are confined to the valence band, which represents a band of energy levels.
When a valence electron gains enough energy, it can move from the valence band to the conduction band.
The energy difference between the valence and conduction bands is called the band gap.
In materials with a large band gap, electrons have difficulty moving to the conduction band, leading to poor conductivity.
Insulators have a large band gap, preventing electron movement, while semiconductors have a smaller band gap.
In conductors like copper, there is no band gap; the conduction band and valence band overlap, allowing free electron movement.
Current carriers in semiconductors include free electrons and holes, and they are responsible for producing current.
Intrinsic silicon crystals are formed through covalent bonding, where silicon atoms bond with adjacent atoms.
At room temperature, silicon gains heat energy that allows valence electrons to move into the conduction band.
When electrons jump to the conduction band, vacancies known as holes are left in the valence band.
Electron current is produced when thermally generated free electrons move towards the positive end of a voltage source.
Hole current is created when electrons in the valence band move into nearby holes, contributing to overall current flow.
Transcripts
In this video, we are going to discuss about band gap and semiconductor current carriers,
which will help us understand how current is produced in a semiconductor.
If we recall some basic topics in chemistry, we’ll remember that all atoms consist of
neutrons, protons, and electrons, except for a normal hydrogen atom which doesn’t have
a neutron.
Using the Bohr model, we can visualize that an atom has a central nucleus consisting of
protons and neutrons that is surrounded by orbiting electrons.
The orbits surrounding the nucleus are grouped into energy levels known as shells and the
outermost shell is called the valence shell.
The valence shell of an atom represents a band of energy levels, which is why it’s
also called a “valence band” and valence electrons are confined to that band.
When a valence electron gains enough energy from an external source, it can escape from
the valence band and goes to the conduction band.
Band Gap The difference in energy between the valence
band and the conduction band is called “band gap”.
It is the amount of energy a valence electron must possess so that it can jump from the
valence band to the conduction band, wherein the electron is free to move throughout the
material.
If the band gap is really big, electrons will have a hard time jumping to the conduction
band, which is the reason of material’s poor conductivity.
Energy Diagrams Let’s try to examine the energy diagram
of the three types of materials used in electronics and discuss the conductivity of each material
based on their band gap.
As we can see, the band gap between the valence band and conduction band in an insulator is
really big.
That is why it doesn’t conduct current.
The band gap in a semiconductor is smaller compared to an insulator and allows valence
electrons in the valence band to jump into the conduction band if it receives external
energy.
In a conductor, like copper, there’s no band gap.
Actually, the conduction band and valence band overlaps, which means that electrons
can freely move into the conduction band.
This is why you may hear the electrons in metal referred to as a “sea of electrons”
- they’re just floating around.
Current Carriers Now that we know more about band gap, let’s
discuss the two types of current carriers in a semiconductor, free electrons and holes,
and see how they produce current in a semiconductor.
Atoms may combine to form a solid crystalline material through covalent bonding.
For example, a silicon atom covalently bonds with four adjacent silicon atoms to form an
intrinsic silicon crystal.
Intrinsic because it doesn’t contain impurities and a crystal because there is a pattern in
how the atoms are connected.
Electron Current At room temperature, intrinsic silicon crystal
gains enough heat energy that enables some of the valence electrons to jump into the
conduction band, becoming free electrons.
When this happens, vacancies are left in the valence band within the crystal.
These vacancies are known as holes.
Now, if we put a voltage source across an intrinsic silicon material, the thermally-generated
free electrons in the conduction band will be attracted to the positive end of the voltage
source.
They will move toward the positive end and this movement produces current in the material.
This type of current is called electron current.
Hole Current While electron current happens in the conduction
band, the other type of current, hole current, happens in the valence band.
Remember that as valence electrons jumped into the conduction band, vacancies or holes
are left in the valence band.
Electrons that remain in the valence band can move into a nearby hole when it receives
a small amount of energy.
This movement produces a current in the valence band called hole current.
Though the current is produced by valence electrons moving into a nearby hole, it is
called hole current so that it won’t be confused with the electron current produced
in the conduction band.
In this video, we learned about band gap and the current carriers in a semiconductor.
We examined the energy diagram of the three types of materials used in electronics, insulators,
semiconductors, and conductors and briefly discussed their conductivities.
We also talked about the two types of semiconductor current carriers, free electrons and holes,
and mentioned how they produce current in a semiconductor material.
If you have any questions, leave it in the comments below and if you’ve found this
interesting or helpful, please subscribe to our channel and like this video!
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