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Intrinsic Semiconductor, also known as i-type or undoped semiconductor, is a pure semiconductor where the number of free electrons and holes are equal. The conductivity of the intrinsic semiconductors becomes zero at room temperature based on the energy band phenomenon.
The number of excited electrons, in intrinsic semiconductors, is equivalent to its number of holes; that is, n = p. Silicon and germanium are one of the two instances of i-type semiconductors and they belong to the IVth Group of the periodic table. The atomic numbers of Silicon and Germanium are 14 and 32 respectively. Intrinsic Semiconductors behave like an insulator at absolute zero.
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Key Terms: Semiconductors, Intrinsic Semiconductors, Diode, Electrons, Silicon, Germanium, Conductivity, i-Type Semiconductors
What is Semiconductor?
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Semiconductors are materials that possess conductivity between conductors (typically metals) and non-conductors or insulators (like paper and glass). These are compounds like Gallium Arsenide or pure elements (including Germanium or Silicon). Semiconductor is a substance with specific electrical properties enabling it to fucntion as a foundation for computers and other electronic devices.
There are two types of semiconductors:
- Intrinsic Semiconductor
- Extrinsic Semiconductor
Intrinsic and Extrinsic Semiconductor
Examples of Semiconductors
Some of the most common semiconductors are Gallium arsenide, germanium, and silicon. Silicon is widely used in Electronic circuit fabrication, while Gallium arsenide is used in laser diodes, solar cells, and more.
Difference between Intrinsic and Extrinsic Semiconductors
There are numerous differences between Intrinsic Semiconductors and Extrinsic Semiconductors. Some of them include:
| Parameter | Intrinsic Semiconductor | Extrinsic Semiconductor |
|---|---|---|
| Meaning | Intrinsic Semiconductors are conductors found in its pure form. | If a chemical impurity is added to an intrinsic semiconductor, then it is called Extrinsic Semiconductor. |
| Classification | No classification. | Depending on the impurity, Extrinsic semiconductors can be classified into two types: n-type and p-type semiconductors. |
| Doping | No doping or additional impurity. | Small amounts of impurity is added in a pure conductor. |
The video below explains this:
Semiconductors and Insulators Detailed Video Explanation:
Also Read:
| Topic Related Links | ||
|---|---|---|
| Transistor | Semiconductor Diode | P n Junction |
| Zener Diode | Integrated Circuits | Application of Junction Diode |
What is Intrinsic Semiconductor?
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An intrinsic semiconductor can be defined as a semiconductor which is exceedingly pure.
- Intrinsic semiconductor is pure in nature and is free of any impurities. It has an equal number of holes and free electrons.
- Some of the most used intrinsic semiconductors are Germanium and silicon.
- As per the energy band theory, the conductivity of an intrinsic semiconductor is going to be zero at ambient temperature.
- Two examples of intrinsic semiconductors are Si and Ge.
Intrinsic Semiconductors
- The properties of the material determine the number of holes and free electrons in a semiconductor and not the impurities added.
- As they do not have any impurity in them, they are sometimes called undoped semiconductors or i-type semiconductors.
- The number of holes and the number of excited electrons is equal for intrinsic semiconductors.
- If n is the number of holes and p is the number of excited electrons in an intrinsic semiconductor, then n = p.
What do intrinsic semiconductors use for conduction at room temperature?Intrinsic semiconductors use Electrons and holes for conduction at room temperature. Exhibit the behavior of intrinsic semiconductors at absolute zero?The intrinsic semiconductor, at absolute zero, typically behaves like an insulator. “An intrinsic semiconductor is doped with trivalent impurity”. Show what happens to it.A p-type semiconductor can be acquired if a trivalent impurity is doped with an intrinsic semiconductor. |
Semiconductor Electronics Class 12 Important Notes PDF
Semiconductor Electronics Class 12 Important Notes
Working Mechanism of Intrinsic Semiconductors
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To understand the working of an intrinsic semiconductor, let’s take the examples of Silicon and Germanium. Below is Germanium and Silicon’s electronic configuration:
| Elements | Atomic Number | Electronic Configuration |
|---|---|---|
| Silicon | 14 | 1s2 2s22p6 3s2 3p2 |
| Germanium | 32 | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2 |
As you can see, both germanium and silicon have four electrons in their outermost shells. Thus,
- When the temperature of the semiconductor is increased, the electrons break free from their shells as they gain more thermal energy.
- There is a vacancy created in the crystal lattice due to the ionization of the atoms and the position from where the electron dislodges creates a hole which has an equivalent positive charge.
- A free electron now occupies this hole due to which another hole is created. Then, this hole also becomes occupied by some free electron and so on.
- In this way, the positive charge is transferred from one position to another.
- The number of holes is equal to the number of free electrons in an intrinsic semiconductor. If “e” is the number of free electrons, “h” is the number of holes, “n” is the total number of atoms present in an intrinsic semiconductor then,
| ne = nh = ni |
Where,
- ni = Number of total intrinsic carrier concentrations
Intrinsic Semiconductor Working
An intrinsic semiconductor behaves differently at different temperatures. For instance, at T = 0K, a semiconductor behaves like an insulator. When T>0, the electrons get excited and jump from the conduction band to the valence band, occupying the conduction band partially. This leaves an equivalent number of holes in the valence bands.
The Movement of Holes
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Another interesting property of semiconductors is that the holes move too, like electrons.
- Due to thermal energy, the electron after being excited breaks itself away from the bond generating a free electron.
- Let’s assume, there are two sites, site 1 and 2.
- At site 1, a vacancy is created there from where the electron releases itself.
- Now, let us consider an electron from site 2 jumps to that vacancy or hole created in site 1. The hole will now move from site 1 to site 2.
- Thus, the electron that has been released from site 1 is not involved in the movement of the hole.
- It rather moves independently like a conduction electron contributing to electron current (Ie) under an applied electric field.
- Moreover, the movement of the hole is basically the movement of the bound electrons.
- These holes move towards a negative potential that generates hole current (Ih) under an electric field. Thus, the total current is I = Ie + Ih.
Checkout Important Handwritten Notes on Semiconductors:
Things to Remember
- A material whose electrical conductivity is between the electrical conductivity of a conductor and insulator is a semiconductor.
- Intrinsic Semiconductor has an equal number of holes and free electrons.
- An intrinsic semiconductor is a semiconductor which is exceedingly pure. Intrinsic semiconductor is free of any impurities.
- Both germanium and silicon have four electrons in their outermost shells. When the temperature of the semiconductor is increased, the electrons break free from their shells as they gain more thermal energy.
- An interesting property of semiconductors is that the holes move as well, like the electrons.
Also Read:
Previous Year Questions
- Diamond is very hard because … [NEET 1993]
- Depletion layer consists of … [NEET 1999]
- For a p-type semiconductor … [NEET 2019]
- A junction diode has a resistance of … [WBJEE 2009]
- A p−n photodiode is made of a material with a band gap of 2eV … [NEET 2008]
- In a semiconductor, the conductivity … [JKCET 2019]
- The following figure represents … [JKCET 2010]
- Which of the following is a semiconductor … [JKCET 2012]
- A n−p−n transistor is connected to common emitter configuration … [NEET 2016]
- Consider the junction diode as ideal … [NEET 2016]
- For the given circuit of p-n junction diode … [NEET 2008]
- If the forward bias voltage in a … [JKCET 2015]
- In breakdown region, a Zener diode behaves as a … [JKCET 2007]
- What is the order of the reverse saturation current … [JKCET 2012]
- What is the name of the level formed due to impurity atom … [JKCET 2003]
Sample Questions
Ques: Which of the following statement is true in an n-type silicon.
(i) The majority of carriers are electrons and dopants are the trivalent atoms.
(ii) Minority carriers are electrons and dopants are the pentavalent atoms.
(iii) Minority carriers are holes and the dopants are the pentavalent atoms.
(iv) Majority carriers are holes and dopants are the trivalent atoms.(1 mark)
Ans: For n-type silicon conductors, the majority carriers are electrons whereas the minority carriers are holes. It is because of the pentavalent atoms that are doped; we get an n-type semiconductor which makes option (c) the correct one.
Ques: Holes diffuse to n–region from p–region in an unbiased p – n junction, because-
(i) They are attracted by the free electrons in the n- region.
(ii) Because of the potential difference, they move across the junction.
(iii) Hole concentration in the p-region is more than that in the n-region.
(iv) All of the above. (1 mark)
Ans: In an unbiased p-n junction, holes disperse from the p-region to the n-region as the concentration of holes in the p region is more as compared to the n region. Hence option (c) is correct.
Ques: The number of silicon atoms per m3 is 5 × 1028. This is doped simultaneously with 5 × 1022 atoms per m3 of Arsenic and 5 × 1020 per m3 atoms of Indium. Calculate the number of electrons and holes. (3 marks)
Ans: Given nI = 1.5 × 1016m–3.
The following values are given in the question:
Number of silicon atoms, N = 5 × 10 28 atom/m3
Number of arsenic atoms, nAS =5×1022 atom/m3
Number of indium atoms, nIN=5×1022 atom/m3
ni=1.5×1016 electron/m3
ne=5×1022 − 1.5×106 = 4.99×1022
Let us consider the number of holes to be nh
In the thermal equilibrium, nenh = ni2
Calculating,
nh=4.51×109
Here, ne>nh,
Therefore the material is an n-type semiconductor.
Ques: What happens when an intrinsic semiconductor is doped with trivalent impurity? (1 mark)
Ans: When a trivalent impurity is doped with an intrinsic semiconductor, a p-type semiconductor is obtained.
Ques: Why n-p-n transistors are preferred over p-n-p transistors? (1 mark)
Ans: The mobility of electrons is higher than the mobility of holes in the n-p-n transistor when compared to the p-n-p transistor.
Ques: For p-type semiconductors which of the statements given is true?
(i) The majority carriers are electrons and dopants are the trivalent atoms.
(ii) Minority carriers are electrons and dopants are the pentavalent atoms.
(iii) Minority carriers are holes and the dopants are the pentavalent atoms.
(iv) Majority carriers are holes and dopants are the trivalent atoms.(1 mark)
Ans- A p-type semiconductor is made by doping trivalent atoms. Also, holes are the majority carriers in p-type semiconductors whereas electrons are minority carriers, which makes option (d) the correct one
Ques: What is an Intrinsic Semiconductor? (1 mark)
Ans: Intrinsic semiconductor is a semiconductor that is considered exceedingly pure. Intrinsic semiconductor is pure in nature and is free of any impurities.
Ques: What is the probability of electrons that can be found in the conduction band of an intrinsic semiconductor at a finite temperature? (3 marks)
Ans: The probability of an electron jumping, at a finite temperature, from the valence band to the conduction band exponentially decreases with an increase in the bandgap (Eg).
Thus,
⇒ \(\frac{1}{1 + e \frac{E- E_F}{KT}}\), K = Boltzmann’s Conduction
P = The probability of determining electron in the conduction band
Therefore, P is decreasing exponentially with an increase in band.
\(\therefore\) E – EF
Ques: Differentiate between semiconductors, conductors and insulators based on its band gap. (5 marks)
Ans: The primary difference between conductors, insulators and semiconductors is mainly on the basis of their relative width of the forbidden energy gaps found in the energy band structures.
In fact, a wide forbidden gap (more than 5eV) can be found for insulators, while a narrow forbidden gap (about 1eV) for semiconductors and absolutely no forbidden gap in the case of conductors.
The valence band and conduction band in conductors is almost close to one another, thus its energy gap is Eg = 0. While in the case of insulators, the energy band gap is found to be extremely high,which can be given by Eg = 6eV. Now, in semiconductors, the Fermi level can be seen to be situated between the valence band and conduction band. Thus, the valence band and conduction band are further separated from one another by an energy gap of 0.1eV.
Apart from the band gap, one of the primary difference between conductor, insulator and semiconductor is that the conductivity of semiconductor can be found to be between the conductivity of insulator and conductor.
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