Since the date of JEE Main is officially announced, the JEE aspirants have already started revising for the test by going through the notes. Among the many chapters in Physics, studying semiconductors is equally important. Semiconductor Electronics is an important part of the Physics syllabus for NEET, JEE and the notes are helpful for all the aspirants preparing for different entrance exams. The Important topics which are included under this chapter i.e. semiconductors are Energy Bands in Solids, p-n junction, logic gates, etc.

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The engineering entrance exams play an important role in getting admission to a university offering engineering courses. Many students have already started revising for JEE Main and thus they need to know the important chapters for JEE Main. Though predicting the most important chapters for JEE Main is quite tougher as many subjects hold significant weightage in the exams.

The notes on semiconductors are very helpful for the JEE Main aspirants. To help the students in saving their savings, we have prepared notes of Semiconductors that will help the JEE aspirants in preparing for JEE Main. 

Must Read: 

• JEE Main Study notes for KTG and Thermodynamics

• JEE Main Study Notes for Electromagnetic waves

Semiconductors

The semiconductors are the material that delivers current, but only partially. The conductivity of these semiconductors lies between conductors, which have full conductivity, and an insulator, which has negligible conductivity. Even the laptops or phones which you are using are actually powered by a bed of silicon covered with billions of transistors thinner than a strand of hair, composed of a solid substance called a semiconductor.

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Energy bands and the flow of electricity

Any crystal is composed of atoms that can hold electrons in a large number of closely spaced energy levels. However, according to Pauli’s exclusion principle, the proof of which goes beyond the scope of this article, demands that only two electrons moving in the opposite directions can harbor a single energy level, making it truly stable. These levels can be shown by lines that are segregated by small distances where electrons are permitted to be located, in these particular levels only. Some of the energy levels are grouped together to form ‘bands’, which are referred to as the energy bands.

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What is an Energy Band?

If the isolated atom the electrons in any orbit result in a fixed amount of energy and outer energy electrons have more energy than their inner, these certain values of energy will be referred to as Energy level, and the atom in solid will be influenced by closely packed neighboring atoms. Therefore, electrons in an orbit of such an atom will arrange energies instead of single energies since the electron revolves under the influence of various forces so the range of energies possessed by an electron is called energy band.

The semiconductors have crystalline structure and are formed by a covalent bond.

What are the types of energy bands?

There are three kinds of energy bands in a solid including the Valence energy band, the Conduction energy band, and the Forbidden energy gap.

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N-Type Semiconductor

When a Pentavalent semiconductor is added in a pure semiconductor like impurity it is called the donor impurity. Free electrons are the majority charge carrier while the holes are minority charge carriers, such semiconductors are known as N-type Semiconductor.

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P-Type Semiconductor

In case a trivalent impurity is added in a semiconductor, it is then referred to as acceptor impurity or holes. The hole is the majority charge carrier and the free electron is a minority charge carrier such type of semiconductor is referred to as P-Type Semiconductor.

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P-N Type Semiconductor

A PN junction diode is created on a single crystal of semiconductor by injecting P type and N-type impurity from different ends.

• As the PN Junction diode is created, the major charge carrier diffuses from a higher concentrated region to the region lower concentration with current flows it is called diffusion current and it moves from P to N.

• Due to Diffusion Electrons combine again with the holes near the junction .Therefore a depletion layer is formed where free electrons and holes are not present.

• The main difference across the depletion layer is known as a potential barrier and developed electric field barrier and the Developed electric field is called junction field.

• In the starting, diffusion current is very large but as depletion region will grow diffusion, the current will decrease and drift current will increase and after a very short time diffusion current and drift currently becomes equal. The net current will be zero and a constant depletion region will be formed.

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Important definitions of Solid and Electronic Device

Thermionic emission 

Thermionic emission is a phenomenon where the electrons are produced by a metal containing free electrons and behave like the molecules of a perfect gas.

Richardson Equation 

 I = AT1/2e-b/T. In this equation, I mean the thermionic current density in amp per sq meter whereas T is the temperature on the kelvin scale. Here, both A and b will remain constant.

A = ne√k/2πm, b = e?/k

Here, n is the total number of electrons per unit volume, e is the charge on the electron, m is the mass of the electron, k is the Boltzmann’s constant.

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Energy gap or Band gap (Eg)

• The least energy required to shift electrons from valence band to conduction band is referred to as the bandgap (Eg)
• The forbidden energy gap between the valence band and the conduction band is referred to as bandgap (Eg).
• Like the way, there are energy levels F electrons in an atom, similarly there are three specific energy bands for the electrons in the crystal formed by these atoms as shown in the figure,
• Completely filled energy bands- The energy band, where most of the electrons are present according to capacity are referred to as completely filled banks.
• Partially filled energy bands- The energy band, where the number of electrons present is lesser as compared to the capacity of the band, then it is referred as the partially filled energy band.
• Electric conduction is possible only in those solids that have an energy band or partially filled an energy band.

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What are the kinds of solids?

Based on the band structure of crystals, solids are segregated in three categories including:

• Insulators
• Semi-conductors
• Conductors

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Why are semiconductors special?

Semiconductors allow the flow of electrons through a substance; the conductivity of conductors is the maximum while it is lowest for an insulator, as the electrons flowing through it are negligible. However, similar to its name, the conductivity of a semiconductor is moderate.

Another amazing point about a semiconductor is that the current is carried not only by electrons, but also by the vacancies they leave behind, which are referred to as the holes. The holes left behind in the valence band can be occupied by electrons from lower states and they play an important role in contributing to the flow of current, thus leaving a hole in these deeper states as well, which will be occupied by electrons beneath, and so on.

Applications of Semiconductors

Let us discuss the uses of semiconductors in our routine lives. Semiconductors are used in most electronic devices, as without them, it would not be easier to live a comfortable life.

Reliability, compactness, low cost and controlled conduction of electricity are some of the features of semiconductors that make them ideal to be used for various purposes in a wide range of components and devices. Even the transistors, diodes, integrated chips, etc. are made using semiconductors.

Uses of Semiconductors in our routine lives

• Temperature sensors are made using semiconductor devices.
• Semiconductors are useful in 3D printing machines
• They are used in the making of microchips and self-driving cars
• Also used in calculators, solar plates, computers and other electronic devices.
• Transistors and MOSFETs used as a switch in Electrical Circuits are designed with the help of semiconductors.

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Previous year questions

Question: Under the forward bias arrangement of a PN-junction diode?

1. The N-end will be connected to the positive terminal of the battery 
2. The P-end will be connected to the positive terminal of the battery
3. The direction of the current will be from N-end to P-end in the diode
4. The P-end will be attached to the negative terminal of battery

Question. The cut-in voltage for silicon diode is almost

1. 0.2 V

2. 0.6 V

3. 1.1 V

4. 1.4 V

Question. The electrical circuit which is used to get smooth dc output from a rectifier circuit is referred to as

1. Oscillator

2. Filter

3. Amplifier

      4. Logic gates

Question: The electrical resistance of the depletion layer is large because

1. It has no charge carriers

2. It has a large number of charge carriers

3. It contains electrons as charge carriers

4. It has holes as charge carriers

Question: In the circuit given below, the value of the current is

1. 0 amp

2. 10−2 amp

3. 102 amp

4. 10−3 amp

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Tips to prepare Semiconductors subject in JEE Main

• While studying Semiconductors, the aspirants must go through the NCERT books thoroughly; before referring to some other books.
• Don’t study all the time, rather you must utilize your time in some other kinds of activities as well. You can play games as it will help you to have a good command on logic gate tables and semiconductor gate workings.
• Include game challenging activities as part of your leisure and utilize your free time in a more productive and fun learning way.
• Learn the basic concepts, and memorize the block diagrams so that you can get a deeper understanding of the subjects and concepts. The chapters mentioned in the semiconductors are generally conceptual and easy topics go for them once you have hold on other difficult concepts.

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Understanding formula and shortcuts are important

For the numerical question, the aspirants need to mug up the formula that can help in increasing the overall score, also you can directly come to the answer quickly and hence helps you in saving time. If you consider the logic or derivation, you automatically can come to the result.

Eliminating the wrong answers to get the right one

By removing the wrong answers with your smart guessing, you can easily come to the right options. Always remember that by removing the options that you are sure can't be right, will help you to arrive at the correct answer in an easier and time-saving way.

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Important Tips to Remember

The JEE Main paper is divided over the entire JEE Main Physics syllabus including questions from different topics. Out of the total 30 questions, 14 questions are easy, 9 questions are medium while the remaining 7 questions are difficult. Any student who focused more on the NCERT books can easily score well in the exam.

• Focus on NCERT books and consider them as the main priority for JEE Main 2020.

• Do a lot of practice and solve more MCQs.

• Analyze last year question paper

• Take mock tests regularly as it will help a lot in improving your scores.

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Some of the books for JEE Main that will help in your exam preparation:

NCERT textbooks & examples and last year’s JEE MCQs for JEE Main 2020 Physics preparation are very important books.

• A book written by H.C Verma “concept of physics vol I and II”, I.E. IRODOV “Problems in general physics” are important

• Halliday, Resnick & Walker “Fundamentals of Physics” for further studies, concept clarity and problem-solving can be considered

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Preparation Tips for the exam

• First of all, read all the questions carefully and then start answering those questions that are easiest for you. Start filling the OMR sheet side by side by doing the familiar questions first.
• Don’t do the guesswork as it might lower your overall scores and can prove dangerous for you.
• Stay calm, don't panic during the examination as it will negatively affect your performance.
• Stay positive, you will surely win the game.

JEE Main Semiconductors FAQs