Conductors, Semiconductors And Insulators

Slide 1: Conductors, Semiconductors and Insulators - INTRODUCTION

In solid-state physics, materials are classified into three categories based on their electrical conductivity: conductors, semiconductors, and insulators.
Conductors are materials that allow electric current to flow easily. They have a high number of free electrons that are available to move in the presence of an electric field.
Semiconductors have intermediate conductivity, with a number of free electrons between that of conductors and insulators. They can be modified to act as conductors or insulators by controlling the doping level or temperature.
Insulators have very low conductivity and do not allow the flow of electric current. They have a completely filled valence band and a large band gap between the valence and conduction bands.

Slide 2: Conductors

Conductors have a high number of free electrons in their conduction band.
In metals, the valence band is partially filled, which allows the electrons to move freely and conduct electricity.
Examples of good conductors include copper, aluminum, silver, and gold.
Conductors also have low resistance, which means they dissipate very little energy in the form of heat.
The conductivity of a conductor can be increased by decreasing its length, increasing its cross-sectional area, or using materials with higher conductivity.

Slide 3: Semiconductors

Unlike conductors, semiconductors have a smaller number of free electrons in their conduction band.
The valence band is partially filled, but the conduction band is partially empty.
The conductivity of semiconductors can be modified by doping, which involves adding impurity atoms to the crystal lattice.
Two types of doping are commonly used: n-type doping (adding atoms with extra electrons) and p-type doping (adding atoms with missing electrons).
Silicon and germanium are widely used semiconductors.

Slide 4: Insulators

Insulators have a completely filled valence band and a large energy gap between the valence and conduction bands.
This energy gap is so large that electrons cannot gain enough energy to jump to the conduction band, making insulators poor conductors of electricity.
Examples of insulators include rubber, glass, wood, and plastic.
Insulators are widely used for electrical insulation, preventing the flow of current where it is not desired.
Insulators can be damaged if subjected to high voltages or temperatures.

Slide 5: Conductivity and Resistivity

Conductivity (σ) is a measure of a material’s ability to conduct electric current.
It is the reciprocal of resistivity (ρ), which is a measure of the opposition offered by a material to the flow of electric current.
The SI unit of conductivity is siemens per meter (S/m), and the SI unit of resistivity is ohm-meter (Ω.m).
Conductivity and resistivity are related by the equation: σ = 1/ρ.
Materials with high conductivity have low resistivity, allowing electric current to flow easily.

Slide 6: Band Theory of Solids

The behavior of conductors, semiconductors, and insulators can be explained using the band theory of solids.
According to this theory, electrons in solids are distributed in energy bands: the valence band and the conduction band.
The valence band is the highest energy band that contains electrons at absolute zero temperature.
The conduction band is the energy band above the valence band, and it is empty at absolute zero temperature.
The band gap is the energy difference between the valence and conduction bands.

Slide 7: Valence Band and Conduction Band

In conductors, the valence band is partially filled, and there is no or a small band gap between the valence and conduction bands.
In semiconductors, the valence band is partially filled, and there is a small band gap between the valence and conduction bands.
In insulators, the valence band is completely filled, and there is a large energy gap (band gap) between the valence and conduction bands.
Electrons in the valence band are tightly bound to their respective atoms, while electrons in the conduction band are free to move.

Slide 8: Effect of Temperature on Conductivity

As temperature increases, the conductivity of conductors generally decreases due to increased scattering of free electrons.
Semiconductors show an increase in conductivity with temperature due to the increased number of thermally excited electrons.
Insulators also have an increase in conductivity with temperature, but it is much smaller compared to semiconductors.
At extremely high temperatures, semiconductors can become conductors, and insulators can become semiconductors.

Slide 9: Examples of Applications

Conductors find applications in electrical wiring, electric circuits, and in the construction of electrical devices.
Semiconductors are commonly used in electronic devices such as transistors, diodes, and integrated circuits.
Insulators are used for electrical safety, insulation of wires, and the construction of insulating materials such as electrical cables and insulating coatings.
The classification of materials into conductors, semiconductors, and insulators is crucial for understanding and designing electronic devices.

Slide 10: Summary

Conductors, semiconductors, and insulators are categories of materials based on their electrical conductivity.
Conductors have high conductivity, semiconductors have intermediate conductivity, and insulators have low conductivity.
Conductivity is determined by the number of free electrons and their ability to move in the presence of an electric field.
The behavior of materials can be explained using the band theory of solids, which involves the valence band, conduction band, and band gap.
The classification of materials is essential in various applications, including electrical wiring, electronic devices, and insulation.

Conductivity and Resistivity

Conductivity is a measure of a material’s ability to conduct electric current.
Resistivity is a measure of the opposition offered by a material to the flow of electric current.
Conductivity and resistivity are inversely related: σ = 1/ρ.
Conductivity is expressed in siemens per meter (S/m).
Resistivity is expressed in ohm-meter (Ω·m).

Factors Affecting Conductivity

Temperature: Conductivity generally decreases with increasing temperature due to increased electron scattering.
Cross-sectional Area: Increasing the cross-sectional area of a conductor increases its conductivity.
Length: Decreasing the length of a conductor increases its conductivity.
Material Selection: Materials with higher conductivity have higher overall conductivity.

Factors Affecting Resistivity

Temperature: Resistivity generally increases with increasing temperature due to increased atomic vibrations.
Impurities: Impurities in a material can increase resistivity by disrupting the regular crystal lattice.
Alloys: Alloys can have lower resistivity compared to pure metals, making them better conductors.
Material Properties: Resistivity is an inherent property of a material and depends on its atomic structure.

Ohm’s Law

Ohm’s Law states that the current passing through a conductor is directly proportional to the voltage applied, and inversely proportional to the resistance.
Mathematically, Ohm’s Law can be expressed as: V = IR, where V is the voltage, I is the current, and R is the resistance.
This law applies to conductors that obey Ohm’s Law, which includes most metallic conductors at normal temperatures.

Power in Electric Circuits

The power dissipated in a resistor can be calculated using the equation: P = IV, where P is the power, I is the current, and V is the voltage across the resistor.
Power is measured in watts (W).
In a circuit, power can be transferred from one component to another, or it can be dissipated as heat in resistors.
Understanding power is crucial for designing circuits and optimizing energy usage.

Superconductivity

Superconductivity is a phenomenon where certain materials exhibit zero electrical resistance at very low temperatures.
Superconductors can conduct electric current indefinitely without any energy loss.
Below a critical temperature called the superconducting transition temperature (Tc), a superconductor exhibits superconducting properties.
Superconductors have numerous applications, including in energy transmission, magnetic levitation, and particle accelerators.

Band Gap in Semiconductors

Semiconductors have a band gap, which is the energy difference between the valence band and the conduction band.
The band gap determines whether a material is a semiconductor or an insulator.
Intrinsic semiconductors have a small band gap and can be modified through doping.
Doping introduces impurities to increase either the number of free electrons (n-type) or the number of holes (p-type) in the material.

Doping in Semiconductors

Doping is the intentional introduction of impurity atoms into a semiconductor crystal lattice.
N-type doping involves adding atoms with extra electrons, such as phosphorus or arsenic, which become the majority carriers.
P-type doping involves adding atoms with missing electrons, such as boron or gallium, which create holes as the majority carriers.
Doping changes the conductivity and electrical properties of semiconductors, making them suitable for various electronic devices.

PN Junction Diode

A PN junction diode is a basic semiconducting device formed by joining a p-type semiconductor with an n-type semiconductor.
The p-side of the diode is called the anode, and the n-side is called the cathode.
The PN junction diode allows current to flow in one direction (forward biased) but blocks current in the opposite direction (reverse biased).
It has various applications, such as rectification, signal modulation, and voltage regulation.

Summary

Conductivity and resistivity are key properties of materials that determine their ability to conduct electric current.
Factors affecting conductivity include temperature, cross-sectional area, length, and material selection.
Factors affecting resistivity include temperature, impurities, alloys, and material properties.
Ohm’s Law relates voltage, current, and resistance in a conductor.
Power in electric circuits is calculated using P = IV.
Superconductivity is a phenomenon with zero electrical resistance at low temperatures.
Semiconductors have a band gap and can be modified through doping and used in electronic devices.
PN junction diodes have applications in rectification, modulation, and voltage regulation.

Slide 21: Energy Band Diagram

Energy band diagrams are used to visualize the energy levels of electrons in a solid.
The horizontal axis represents the position in the material, while the vertical axis represents the energy level.
The valence band is the lower energy level occupied by electrons, while the conduction band is the higher energy level that can be occupied by electrons.
The band gap is the energy difference between the valence and conduction bands.

Slide 22: Conductivity in Metals

The high conductivity of metals is due to the presence of a partially filled valence band and overlapping conduction bands.
Electrons in the valence band are loosely held and can easily move in response to an electric field.
These electrons are referred to as free electrons, and they contribute to the overall conductivity of the metal.
The high density of free electrons in metals results in their high conductivity.

Slide 23: Intrinsic Semiconductors

Intrinsic semiconductors are pure semiconducting materials without any intentional doping.
They have a small band gap that requires an input of energy to promote electrons from the valence band to the conduction band.
At absolute zero temperature, intrinsic semiconductors have very few free electrons in the conduction band.
However, as the temperature increases, thermal energy excites some electrons into the conduction band, increasing the conductivity.

Slide 24: Extrinsic Semiconductors - N-type

N-type semiconductors are created by doping the intrinsic semiconductor with impurity atoms that have more valence electrons.
Examples of impurity atoms used for n-type doping are phosphorus, arsenic, and antimony.
These impurity atoms introduce additional electrons into the material, creating an excess of negative charges.
The extra electrons in n-type semiconductors become the majority carriers and significantly increase the conductivity.

Slide 25: Extrinsic Semiconductors - P-type

P-type semiconductors are created by doping the intrinsic semiconductor with impurity atoms that have fewer valence electrons.
Examples of impurity atoms used for p-type doping are boron, aluminum, and gallium.
These impurity atoms create a deficiency of electrons, known as holes, in the semiconductor crystal lattice.
The holes in p-type semiconductors become the majority carriers and contribute to the conductivity.

Slide 26: PN Junction and Diode Operation

A PN junction is formed when a p-type semiconductor is brought into contact with an n-type semiconductor.
This junction forms a depletion region due to the migration of free electrons and holes across the junction.
When a forward bias voltage is applied, the depletion region decreases, allowing current flow through the diode.
In reverse bias voltage, the depletion region widens, preventing significant current flow through the diode.

Slide 27: Diode Characteristics

The current-voltage (IV) characteristics of a diode exhibit different behaviors depending on the bias voltage.
For forward bias, the diode has a low resistance, and current flows easily.
For reverse bias, the diode has a very high resistance, and only a small leakage current is present.
The forward voltage drop across a diode is usually around 0.7 V for silicon diodes and 0.3 V for germanium diodes.

Slide 28: Semiconductor Devices

Semiconductors are the foundation of modern electronic devices.
Transistors are the building blocks of digital electronics and amplifiers.
Diodes are used for rectification, voltage regulation, and signal modulation.
Integrated circuits (ICs) are made up of numerous semiconductor devices on a single chip and are used in various applications, including computers, smartphones, and electronic systems.

Slide 29: Applications of Insulators

Insulators have very low conductivity and are used to prevent the flow of electric current.
Insulators are widely used in electrical systems for insulation and safety, such as in electrical cables, switches, and insulation materials.
They provide protection against electric shocks and minimize energy loss.
Insulators can be made from a variety of materials, including rubber, plastic, glass, and ceramic.

Slide 30: Summary

Energy band diagrams help visualize the energy levels of electrons in solids.
Conductivity in metals is due to the presence of free electrons in the valence and conduction bands.
Intrinsic semiconductors have a small band gap and require thermal energy to promote electron movement.
Extrinsic semiconductors, such as n-type and p-type, are created through intentional doping.
The PN junction creates a diode with specific operational characteristics.
Semiconductors play a crucial role in various electronic devices and integrated circuits.
Insulators have low conductivity and are used for electrical insulation and safety purposes.