NCERT Class 12 Physics Chapter 14 Notes Semiconductor Electronics Materials Devices and Simple Circuits - Download PDF

This class 12 physics chapter 14 notes provides an introduction to the complex world of materials, devices, and simple circuits that power today's technological landscape. As you embark on this enlightening journey, you will discover the mysteries of metal, semiconductor, and insulator classification, as well as delve deeply into solid band theory.

But wait—there's more! Beyond its relevance to board exams, this chapter contains the keys to success in prestigious engineering and medical entrance exams such as JEE, NEET, WBJEE, BCECE, and others. These Semiconductor Electronics - Materials, Devices and Simple Circuits class 12 notes, which cover topics such as intrinsic and extrinsic semiconductors and the formation of p-n junctions, are more than just a study aid; they are a passport to academic excellence.

What's even better? These invaluable insights are conveniently packaged in a downloadable PDF format, allowing students to access and use them offline, anytime, anywhere, and for free. So, prepare to unlock the secrets of semiconductor electronics and boost your learning experience with CBSE class 12 physics ch 14 notes!

Also, students can refer,

• NCERT Notes Class 12 Physics
• NCERT Solutions for Class 12 Physics Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits
• NCERT Exemplar Class 12 Physics Chapter 14 Solutions Semiconductor Electronics: Materials, Devices and Simple Circuits

NCERT Class 12 Physics Chapter 14 Notes

Earlier electronic devices were made up of vacuum tubes or valves.

Vacuum tubes or Valves:

• The evolution of vacuum tubes started with diodes and proceeded to date with triode, tetrode and pentode.

• Valves are responsible for controlling the flow of electrons. In diodes there used to be two electrodes i.e. cathode and anode.

• Similarly, triode used to have three electrodes i.e. cathode, grid and anode and tetrode used to have four electrodes i.e. anode, two grids and cathode and pentode used to have five electrodes i.e. anode, three grids and cathode.

• In vacuum tubes, the electrons are produced by heating the cathode using a low tension battery. The vacuum helps the electron not to lose its energy by collision with air molecules in the way.

• The disadvantages of vacuum tube devices are that they used to be

1. Huge

2. Operate at high voltages

3. Consume a lot of power

4. Have restricted life

5. Low responsibility

Diodes and transistors

• After that, the invention of semiconductor junction was there particularly, junction diode and transistors

• They replaced the vacuum tubes or valves.

• The blessings of semiconductor devices square measure that they're

1. tiny in size

2. Operate at low voltages

3. Consume tiny power

4. Long life

5. High dependability

• The circuits consisting of transistors were still large, less shockproof.

• This diode to the invention of integrated circuits that may be a major revolution within the electronic business

For example, the sooner generation Tv and laptop monitors were terribly large as they were supported the principle of vacuum tubes. However today, we've LCD (Liquid Crystal Display) monitors that support solid-state physics.

Classification of Metals, Semiconductors and Insulators

On the idea of physical phenomenon

According to the physical phenomenon of cloth, we will simply tell whether or not it is classified as metals, semiconductors or insulators.

The electrical physical phenomenon is mostly diagrammatic by σ whereas the reciprocal of physical phenomenon is electric resistance and is diagrammatic by ρ = 1/σ

● Metals – Metals have high physical phenomenon and low electric resistance

The order of ρ is 10^-2 to 10^-8 Ω m

The order of σ is 10² to 10⁸ S/m

• Semiconductors – They have conductivity and resistivity in between metals and insulators.

The order of ρ is 10^-5 to 10^-6 Ω m

The order of σ 10⁵ to 10⁶ S/m

• Insulators – They have high resistivity and hence low conductivity.

The order of ρ is 10^-11 to 10^-19 Ω m

The order of σ 10² to 10¹⁹ S/m

Classification of semiconductors

The semiconductors can be classified into two types i.e. Elementary kind semiconductor and compound kind semiconductor.

Elementary type semiconductor – These types of semiconductors are available in natural form for example Silicon (Si) and germanium (Ge)

• Compound type semiconductor – When semiconductors are made by compounding the metals, compound type semiconductor is obtained. Further, they can be classified into

1. Inorganic semiconductors like CdS, GaAs etc

2. Organic semiconductors like Anthracene, doped phthalocyanines

3. Organic polymers – Polypyrrole, polyaniline, polythiophene

Band Theory of Solids

The energy levels of the atom form a nonstop band, wherever the electrons move This is known as the band theory of solids.

• In an atom, the protons and the neutrons constitute the central part called the nucleus.

• The electrons revolve around the nucleus in definite orbits.

• The orbits are named as 1s, 2s, 2p, 3s, 3p, 3d etc. each of which features totally different energy.

• All electrons of the same orbit will have the same energy.

• The electrons within the innermost orbits that are fully crammed are valence electrons whereas the electrons within the outermost orbit that don't fully fill that shell are known as conduction electrons.

Classification on The Basis of Energy Bands

• Depending upon the relative position of the valence band and the conduction band, the solids are classified into three categories i.e. conductors, insulators and semiconductors.

Conductors

• The conduction band and also the valence band part overlap one another and there's no impermissible energy bandgap in between.

• The electrons from the valence band can easily move into the conduction band.

• A large number of electrons are available for conduction.

• The resistance of such materials is low but the conductivity is high.

Insulators

• In insulators, there is a large energy gap between the valence band and the conduction band.

• The energy gap is very high such that the electrons from the valence band cannot move to the conduction band by thermal excitation.

• As there are no electrons in the conduction band, electrical conduction is not possible.

Semiconductors

• A finite but small energy gap exists between the valence band and the conduction band.

• At room temperature, some of the electrons from the valence band acquire energy and move into the conduction band.

• At high temperatures semiconductors have conductivity. The resistance is not as high as in insulators.

Types of Semiconductors

We have two types of semiconductors, these are Intrinsic semiconductors and Extrinsic semiconductors.

Intrinsic semiconductor

• A pure semiconductor that is free from impurities is called an intrinsic semiconductor.

• The electrical conductivity of a pure semiconductor is known as intrinsic conductivity.

Crystalline structure

At temperature 0K

• In the crystal structure, the four valence electrons of the Ge atom form four covalent bonds by sharing electrons with its neighbouring atoms.

• Each covalent bond is made of two atoms, one from each atom.

At room temperature

• The conduction takes place only if the electrons break away from the covalent bonds and are free by the thermal energy.

• The electron breaks away from the covalent bond and the empty space or vacancy left in the bond is called a hole.

• An electron can break away and can be attracted by the hole, from the neighbouring atom, creating hole in the other place.

• In the crystal structure, we can see that the electrons break the covalent bond and keep moving. Similarly, due to the attraction of holes and electrons, holes also keep moving in a crystal.

• As a result, the breakage of a covalent bond produces one free electron and one hole in the crystal.

• In an intrinsic semiconductor, the number of holes is equal to the number of electrons.

Energy band theory

The energy gap between the valence and the conduction band is of about 1 eV.

At temperature 0K –

• The valence band is full and the conduction band is totally empty.

• Since there are no electrons available for conduction, the Ge crystal behaves like an electrical insulator.

At room temperature -

• The electrons in the valence band get energy from the thermal vibrations of the atoms to cross the energy gap and move into the conduction band as free electrons.

• This results in the electrical conductivity of the semiconductor.

• A vacancy is created in the valence band as electrons move from the valence band to the conduction band. This vacancy is understood as a hole.

• The holes move in the valence band and electrical conduction in semiconductors is possible, as electrons move in the conduction band.

• When an electric field is applied, the holes move towards the negative potential, giving rise to hole current and electrons move towards the positive potential giving rise to electron current at a higher temperature.

Extrinsic semiconductor

• A doped semiconductor or a semiconductor with impurity is called an extrinsic semiconductor.

• There are two types of extrinsic semiconductors i.e. n-type and p-type.

• In n-type semiconductors, we find the electrons as the major carriers while the holes are the minor carriers.

• In p-type semiconductors, we discover holes as the majority carriers whereas the electrons are the minority carriers.

• A detailed study of n-type and p-type semiconductors will help us to understand better the extrinsic semiconductor.

• When pure Si or Ge is doped with a controlled amount of pentavalent atoms, like Arsenic, Phosphorus, Antimony or Bismuth, we get an n-type semiconductor.

• The four valence electrons from the impure atom will combine with four electrons of the Si or Ge atom to form 4 covalent bonds.

• The fifth electron of the impure atom is free to move as a result each atom of the impure substance, donates a free electron for conduction. Hence, it is called a donor atom.

• Giving the free electron for conduction, the impure atom becomes positively charged and as a result, gives rise to a hole.

• So, in n-type semiconductors the electrons square measure the bulk carriers and therefore the holes square measure minority carriers.

Energy band theory

• On scrutiny, Si or Ge doped with impurities like Arsenic with a pure Si or Ge, rock bottom energy of the conduction band may be a smaller quantity.

• The electrons occupy discrete energy levels known as the donor energy level between the valence band and the conduction band.

• We find this donor energy level below the bottom of the conduction band.

p-type semiconductor

• When pure Si or Ge is doped with a controlled amount of trivalent atoms, like Gallium, Indium, Boron or Aluminium, we get p-type semiconductor.

• The three valence electrons from the impure atom will combine with three electrons of the Si or Ge atom to form 3 covalent bonds.

• One unbounded electron in the Ge atom tries to form a covalent bond with the neighbouring Ge atom.

• This Ge-Ge covalent bond creates a deficiency of electrons in the Ge atom creating a hole.

• This hole is compensated by the breakage of Ge-Ge covalent bond in the neighbourhood as a result the electron moves towards the hole, resulting in hole formation at some other place.

• The trivalent atoms are called acceptor atoms whereas the conduction of electricity is due to the motion of holes.

• Thus in p-type semiconductors, holes are the majority carriers whereas electrons are minority carriers.

Energy band theory

• Si or Ge doped with impurities like Aluminium produces an energy level that is situated in the energy gap slightly above the valence band.

• This is known as the acceptor energy level.

• At room temperature, the electrons of the valence band are easily transferred to the acceptor level. This produces an outsized variety of holes within the valence band.

• The valence band becomes the hole conducting the band.

p-n Junction Formation

• A p-n junction is the basic building block of many semiconductor devices like diodes, transistors etc.

• The holes are the majority carriers in the p-type semiconductor whereas the electrons are the majority carriers in the n-type semiconductor.

• In n-type semiconductors, the concentration of electrons is more as compared to the concentration of holes. Similarly, in p-type semiconductors, the concentration of holes is more as compared to the concentration of electrons.

• Diffusion is the first process that occurs in the p-n semiconductor.

• In the formation of the p-n junction, due to the concentration gradient across the p and the n sides, there is the diffusion of electrons from n region and therefore the holes are diffused from the p region to the n region.

Diffusion Current

• It is due to the motion of charge carriers due to the difference in concentration in two regions of the p-n junction, across the junction.

• The diffusion leaves behind a positive charge on the n-side close to the junction. This positive charge known as an ionised donor is immobile due to bonding with the surrounding atoms.

• Similarly, in the p-region near the junction, there is a negative charge or acceptor ions that are immobile.

Depletion region formation –

• The space charge region on both sides of the p-n junction is devoid of any charge carriers and has immobile ions.

• Due to this, it results in the formation of a depletion region near the junction.

Field setup –

• As the depletion region is formed, it results in setting up a field at the junction.

• The field along the junction acts like a fictitious battery that is connected across the junction with a positive terminal connected to the n-region.

Barrier creation –

• The electric field at the junction sets a barrier opposing further diffusion of majority charge carriers through the junction.

• Thus, the barrier that is created at the junction prevents further diffusion.

• Width of the barrier:- The distance from one side of the barrier to the other is called the width of the barrier.

• Height of the barrier:- The potential difference from one side of the barrier to the other side is known as the height of the barrier.

Drift current

• Since the electric field is developed at the junction, the electrons from the p-region move to the n-region. Similarly, the hole from the n-region moves to the p-region. Due to this drift current is produced.

Drift current Vs Diffusion current

• The drift current is in the opposite direction of the diffusion current.

• At a particular stage, the drift current becomes equal to the diffusion current.

• This stage is set to be in an equilibrium state when no current flows across the p-n junction.

• The Potential barrier is maximum and is equal to .

• Thus, a p-n junction is formed and under equilibrium, there is no net current.

• The electrons or holes move a large distance before the collision with another electron or hole when doping concentration is small.

• As a result, the width of the p-n junction becomes large.

• On the contrary, the electric field becomes small as the width of the p-n junction increases.

Forward Biasing

• When we connect the positive terminal of the external battery to the p-side and the negative terminal of the external battery to the n-side, the p-n junction is said to be forward-biased.

• The direction of the applied voltage V is in the opposite direction of the potential barrier setup at the junction.

• The depletion layer width decreases and the barrier height is reduced. The effective barrier height beneath forward bias is.

Reverse Biasing

• When we connect the positive terminal of the external battery to the n-side and the negative terminal of the external battery to the p-side, then the p-n junction is said to be reverse biased.

• The applied voltage is in the same direction of the barrier potential.

• The barrier height increases and the depletion region widens due to change in electric field.

• The effective barrier height is

Application of junction diode as a Rectifier

• The rectifier is a device used for converting alternating current or voltage into direct current or voltage.

• Half-wave rectifier: The figure below represents the half-wave circuit:

• :

Input and output waveform of half-wave rectifier is as follows:

• Full-wave rectifier: The figure below represents the half-wave circuit:

• A p-n junction diode is used both as a half-wave and full-wave rectifier.

• The resistance of a p-n junction diode is low when forward biased and is high when reverse biased.

Special purpose p-n junction diode

Zener Diode

• It is a special purpose diode. It is named after the discoverer C. Zener.

• It is specially designed to operate under reverse bias in the breakdown region.

• The symbol for the Zener diode is

Characteristics:

• Zener diodes have a thin depletion region.

• In between 0.3 to 0.7V, Zener diodes have biased turn-on voltage.

• There will be a leakage in the current flow under reverse mode.

Zener Diode as Voltage Regulators

The above circuit represents Zener diodes as voltage regulators.

Here, Zener voltage should be equal to the load voltage.

The value of the series resistor is Rs=(V_L-V_Z)/I_L where V is voltage, I is current

Optoelectronic Junction Devices

Generally, the semiconductor diodes in which the current carriers are generated by the photons (through photoexcitation) are known as optoelectronic devices.

Some examples of optoelectronic junction devices are – Photodiode, Light-emitting diode and solar cells.

Photodiode – In this, the electron-hole pair is generated due to the illumination of the junction with light. The circuit diagram is shown below:

Photodiodes work based on the photoelectric effect. It operates on the principle that electricity starts to flow when the junction of the two semiconductor devices is illuminated.

V-I characteristic curves of photodiode

Light-emitting diode – This special tangency emits light-weight radiation unendingly once forward-biased properly. The circuit diagram is shown below:

Characteristics:

The light produced by LED is directional.

The efficiency of LED does not depend on the temperature.

They consume less energy and have a longer life.

Solar cell–When solar light falls on a p-n junction, emf is generated which can be used effectively. The circuit diagram is shown below:

I-V chara of solar cell

Junction Transistor

A junction transistor is a semiconductor device with two junctions and three terminals. The junction transistor has 3 doped regions forming 2 p-n junctions.

There are two types of transistors.

(a) n-p-n transistor

(b) p-n-p transistor.

• Emitter and collector can be differentiated on the basis of arrow arrangement.

• The emitter has an arrow pointing inwards or outwards.

• The arrow direction for the NPN transistor is indicated outwards in the emitter.

• The head of the arrow indicates the direction of the conventional current in the transistor.

• On the contrary, the arrow direction for the PNP transistor is indicated inwards in the emitter.

• We obtain a P-N-P transistor by growing a thin layer of n-type semiconductor in between two relatively thick layers of p-type semiconductor.

• We obtain n-p-n transistors by growing a thin layer of p-type semiconductor in between two relatively thick layers of n-type semiconductor.

Digital Electronics – Introduction

Logic Gates

• In digital electronics, we consider only two values of voltage – high voltage that is represented by 1 and low voltage that is represented by 0.

• Logical gates are basically electronic circuits.

• Similar to a gate that controls the flow of vehicles, the logical gates conjointly controls the flow of data supported the logical relations.

● We think about the logic gates are the essential building blocks of digital-physical science.

• We will say a computer circuit could be a digital circuit that follows a logical relationship between the input and output.

• Some of the essential sorts of the logical gates are – NOT, OR, AND, NOR and NAND. Each gate features either one or multiple inputs and outputs.

• Every gate is diagrammatic by a logo.

• The input and output of the logical gate is diagrammatic within the sort of a truth table. The reality table considers all possible mixtures of the input and shows the individual output in each case.

NOT Gate

OR Gate

AND Gate

NOR Gate

NOT+OR

Output =

NAND Gate

NOT + AND gate

Universal gate

The NAND circuit and therefore the NOR gate square measure known as universal gates as any of the Boolean perform may be enforced while not necessary to use the other gate.

Significance of Semiconductor Electronics - Materials, Devices and Simple Circuits notes class 12

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