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Extrinsic Semiconductor

Difference Between Types of Semiconductor

Electron Hole Concentration Calculation

Effect of Temperature on Pure Semiconductor

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Q: Suppose a pure Si crystal has \$5\times 10^{28}\$ atoms \$m^{-3}\$. it is doped by 1 ppm concentration of pentavalent As. Calculate the number of electrons and holes. Given that \$n_{1}=1.5\times 10^{16}m^{-3}\$.

1 atom of Si doped out of \$10^{6}\$ atoms (1 ppm of As)\$ \Rightarrow \$ In \$ 5 \times 10^{28}\$ atoms net doped =\$\frac{5\times10^{28}}{10^{6}} = 5\times 10^{22} \$ atoms1 As atom creates \$1 e^{\circleddash }\$ excenso, no. of excen electron \$ = 5 \times 10^{22} = n_{e}\$also, \$ n_{e}n_{n}=n_{1}^{2}\$\$ \Rightarrow n_{n}=\frac{n_{1}^{2}}{n_{e}} = \frac{(1.5\times10^{16})^{2}}{5\times 10^{22}} = 4.5\times 10^{9}\$\$ \therefore \$ No. of holes formed \$ = 4.5 \times 10^{9}.\$as \$ n_{e} > n_{n} \rightarrow \$ It is a N - type semiconductor formed.

Q: Write down 5 difference between N-type and P-type semiconductors.

Difference between the P and N type semiconductors Sl No P-type Semi conductor N-type semi conductor 1P-type semiconductor is formed due to the dopping of III group elements i.e. Boron, Aluminium, Thallium.N-type semi conductor is formed due to dopping of Nitrogen, Phosporus, Arsenic, Antimony, Bismoth. 2These are also known as Trivalent semi conductors.These are also known pentavalent semiconductor. 3P-type semiconductors is positive type semiconductor it means it deficiency of 1 electron is required.N-type semiconductor is negative type semi-conductor it means excess of 1 electron is required. 4In P-type semiconductor majority charge carries are holes and minority charge carries are electrons.In N-type semiconductor majority charge carries are electrons and minority charge carries are hole. 5A hole indicates a missing electron. In this no. of holes is more than the no. of electrons.In N-type semiconductor the no. of holes is less than the no. of free electron.

Q: In an n-type semiconductor, the Fermi-energy level lies :

For an n-type semiconductor, there are more electrons in the conduction band than there are holes in the valence band. This is due to the doping of donor impurity to form n-type semiconductor. This leads to formation of donor energy level below conduction band in forbidden energy gap, which implies that the probability of finding an electron near the conduction band edge is larger than the probability of finding a hole at the valence band edge. Therefore, the Fermi level is closer to the conduction band in an n-type semiconductor and it lies in the forbidden energy gap nearer to the conduction band.

Q: The number of silicon atoms per \$m^3\$ is \$5\, \times\, 10^{28}\$. This is doped simultaneously with \$5\, \times\, 10^{22}\$ atoms per \$m^3\$ of arsenic and \$5 \times\, 10^{20}\$ per \$m^3\$ atoms of indium. Calculate the number of electrons and holes. Given that \$n_i\, =\, 1.5\, \times\, 10^{16}\ /m^{3}\$. Is the material n-type or p-type?

Number of silicon atoms, \$N=5\times10^{28}\ atom/m^3\$Number of arsenic atoms, \$n_{AS}=5\times10^{22}\ atom/m^3\$Number of indium atoms, \$n_{IN}=5\times10^{22}\ atom/m^3\$\$n_i=1.5\times10^{16}\ electron/m^3\$\$n_e=5\times10^{22}-1.5\times10^6=4.99\times10^{22}\$Let number of holes be \$n_h\$In thermal equilibrium, \$n_en_h=n_i^2\$so, \$n_h=4.51\times10^9\$\$n_e>n_H\$, material is an n-type semiconductor.

Q: A silicon specimen is made into a p-type semiconductor by doping on the average one indium atom per \$5\times 10^7\$ silicon atoms. If the number density of atoms in the silicon specimen is \$5\times 10^{28}\$ atoms\$/m^3\$. Then the number of acceptor atoms in silicon will be.

Number density of atoms in Si\$=\displaystyle 5\times 10^{28}\frac{atoms}{m^3}=5\times 10^{22}\frac{atoms}{cm^3}\$Since \$1\$ atom of indium is doped in \$5\times 10^7\$ silicon atoms,\$\therefore\$ Total number of doped indium atoms\$\displaystyle =\frac{5\times 10^{22}}{5\times 10^7}=1\times 10^{15}\frac{atoms}{cm^3}\$\$\therefore\$ Number of acceptor atoms in silicon\$=\displaystyle 1\times 10^{15}\frac{atoms}{cm^3}\$.

Q: Distinguish between 'intrinsic' and 'extrinsic' semiconductors.

Intrinsic Semiconductor -It is pure, natural semiconductor, such as pure Ge and pure Si . In it the concentrations of electrons and holes are equal.Its electrical conductivity is very low.Its conductivity cannot controlled. Its conductivity increases exponentially with temperatureExtrinsic Semiconductor-It is prepared by adding a small quantity of impurity to a pure semiconductor, such as n-and p-type semiconductors. In it the two concentrations are unequal. There is an excess of electrons in n-type semiconductors and an excess of holes in p-type semiconductors. Its electrical conductivity is significantly high.Its conductivity can be controlled by adjusting the quantity of the impurity added.Its conductivity also increases with temperature, but not exponentially.

Q: In an intrinsic semiconductor, the number of electrons in the conduction band is ________ the number of holes in the valence band.

In an intrinsic semiconductor, the number density of electrons is equal to the number density of holes i.e \$ne=nh\$.Since there is no doping, no extra hole or electron is produced.

Q: Let \$n_p\$ and \$n_e\$ the number of holes and conduction electrons in an intrinsic semiconductor. Then:

In an intrinsic semicondutor, number of holes carriers are equal to number of electrons as no doping is there in intrinsic material.In extrinsic materials, due to doping, numbers of holes are different to those of electrons.So, \$n_p=n_e\$

Intrinsic Semiconductor

8 mins

7 mins

Intrinsic Semiconductor

8 mins

Extrinsic Semiconductor

6 mins

p-type and n-type semiconductor

17 mins

Semiconductor in thermal equilibrium

4 mins

Quick Summary With Stories

Introduction to Intrinsic Semiconductors

3 mins read

Intrinsic Semiconductor

3 mins read

Extrinsic Semiconductor

3 mins read

P-type and N-type Semiconductor

3 mins read

Difference Between Types of Semiconductor

3 mins read

Conceptual Problems on Intrinsic/Extrinsic Semiconductor

2 mins read

Semiconductor in Thermal Equilibrium

2 mins read

Electron Hole Concentration Calculation

2 mins read

Important Questions

Suppose a pure Si crystal has $5 \times 1 0^{28}$ atoms $m^{- 3}$ . it is doped by 1 ppm concentration of pentavalent As. Calculate the number of electrons and holes. Given that $n_{1} = 1.5 \times 1 0^{16} m^{- 3}$ .

Write down 5 difference between N-type and P-type semiconductors.

In an n-type semiconductor, the Fermi-energy level lies :

The number of silicon atoms per $m^{3}$ is $5 \times 1 0^{28}$ . This is doped simultaneously with $5 \times 1 0^{22}$ atoms per $m^{3}$ of arsenic and $5 \times 1 0^{20}$ per $m^{3}$ atoms of indium. Calculate the number of electrons and holes. Given that $n_{i} = 1.5 \times 1 0^{16} / m^{3}$ . Is the material n-type or p-type?

Pure $S i$ at $500 K$ has equal number of electron $(n_{e})$ and hole $(n_{h})$ concentration of $1.5 \times 10^{16} m^{- 3}$ . Doping by indium increases $n_{h}$ to $4.5 \times 10^{22} m^{- 3}$ . The doped semiconductor is of

Hard

NEET

A silicon specimen is made into a p-type semiconductor by doping on the average one indium atom per $5 \times 1 0^{7}$ silicon atoms. If the number density of atoms in the silicon specimen is $5 \times 1 0^{28}$ atoms $/ m^{3}$ . Then the number of acceptor atoms in silicon will be.

If the ratio of the concentration of electrons to that of holes in a semiconductors is $\frac{7}{5}$ and the ratio of currents is $\frac{7}{4}$ , then the ratio of drift velocities is

Distinguish between 'intrinsic' and 'extrinsic' semiconductors.

Easy

In an intrinsic semiconductor, the number of electrons in the conduction band is ________ the number of holes in the valence band.

Easy

Let $n_{p}$ and $n_{e}$ the number of holes and conduction electrons in an intrinsic semiconductor. Then:

Easy