JEE MAIN 2020 NEWS
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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.
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.
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.
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.
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.
There are three kinds of energy bands in a solid including the Valence energy band, the Conduction energy band, and the Forbidden energy gap.
|Valance Energy Band||Forbidden Energy Band||Conduction Energy Band|
|This band has valence electrons.||Zero electrons are there in this band||A few electrons are found|
|This band might be partially or completely filled with electrons.||This is completely empty.||This band will be empty or partially filled with electrons.|
|Here the electrons are not able to gain energy from the external electric field.||Electrons can gain energy from electric fields.||-|
|In this band, the electrons of the outermost orbit of the atom contribute in the formation of the band.||In this band some electrons are obtained by breaking the covalent bands.||-|
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.
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.
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.
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.
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.
Based on the band structure of crystals, solids are segregated in three categories including:
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.
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.
Question: Under the forward bias arrangement of a PN-junction diode?
Question. The cut-in voltage for silicon diode is almost
Question. The electrical circuit which is used to get smooth dc output from a rectifier circuit is referred to as
4. Logic gates
Question: The electrical resistance of the depletion layer is large because
It has no charge carriers
It has a large number of charge carriers
It contains electrons as charge carriers
It has holes as charge carriers
Question: In the circuit given below, the value of the current is
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.
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.
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