The process of adding impurities to a pure semiconductor is called doping. The doped material is referred as extrinsic semiconductor. Doping is done to generate either a surplus or a deficiency in valence electrons.

Suppose a ‘ n ’ -type wafer is created by doping Si crystal having 5 × 10 28 atoms / m 3 with 1 ppm concentration of A s . On the surface 200 ppm Boron is added to create ‘ P ’ region in this wafer.Considering n i = 1 . 5 × 10 16 m – 3 , (i) Calculate the densities of the charge carriers in the n & p regions. (ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.

When A s (pentavalent) is added to S i the n -type wafer is created. So, the number of majority carriers in n - type wafer, N e = N D and D Si = 1 10 6 × 5 × 10 28 = 5 × 10 22 / m 3 For number of minority carriers n h n e × n h = n i 2 n h = n i 2 n e = 1 . 5 × 10 15 × 1 . 5 × 10 16 5 × 10 22 ( n i = 1 . 5 × 10 16 / m 3 ) (Given) = 0 . 3 × 1 . 5 × 10 32 - 22 = 0 . 45 × 10 + 10 electrons per m 3 When boron(trivalent) is implanted in S i crystal, p - type wafer is formed with number of holes, n h = ( N D × n of S i ) = 200 10 6 × 5 × 10 28 = 1000 × 10 28 - 6 n h = 1 × 10 25 per m 3 Minority carrier in p - type water n e × n h = n i 2 n e = n i 2 n h = 1 . 5 × 10 16 × 1 . 5 × 10 16 10 25 = 2 . 25 × 10 7 = 2 . 25 × 10 7 electrons per m 3 When reversed bias is applied on p - n junction then the minority charge carrier moves towards depletion layer i . e . , holes n h = ( 0 . 45 × 10 10 per m 3 ) from n side and n e = 2 . 25 × 10 7 / m 3 from p side moves towards junction and make the depletion layer thicker.

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Important Questions on Electromagnetic Induction

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Give reasons to explain the following:

(i) The core of the transformer is laminated.

(ii) Thick copper wire is used in windings.

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Laminated iron sheets are used to minimize _____ currents in the core of a transformer.

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Draw the diagram of a device which is used to decrease high ac voltage into a low ac voltage and state its working principle. Write four sources of energy loss in this device.

EASY

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What is the phenomenon involved in the working of transformer ?

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What is the magnetic moment associated with a solenoid?

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A domain in ferromagnetic iron in the form of cube is having

5 \times 10^{5}

atoms. If the side length of this domain is

1.5 μm

and each atom has a dipole moment of

8 \times 10^{- 24} A m^{2}

, then magnetisation of domain is

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With the help of a labelled diagram, explain the working of a step-up transformer.

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A power transmission line feeds input power at

2300 V

to a stepdown transformer with its primary windings having

4000

turns. What should be the number of turns in the secondary windings in order to get output power at

230 V

EASY

Physics>Electricity and Magnetism>Electromagnetic Induction>Magnetic Flux

Magnetic susceptibility for a paramagnetic and diamagnetic material is respectively

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Physics>Electricity and Magnetism>Electromagnetic Induction>Magnetic Flux

What is magnetic susceptibility?

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Physics>Electricity and Magnetism>Electromagnetic Induction>Magnetic Flux

A donor impurity results in

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Mobilities of electrons and holes in a sample of intrinsic germanium at room temperature are

0.54 m^{2} v^{- 1} s^{- 1}

and

0.18 m^{2} v^{- 1} s^{- 1}

respectively. If the electron and hole densities are equal to

3.6 \times 10^{19} m^{- 3}

, calculate the germanium conductivity. Take,

e = 1.6 \times 10^{- 19} C

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In a n-type silicon, which of the following statement is true:

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What is doping?

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A semiconductor is known to have an electron concentration of

8 \times 10^{13} {cm}^{- 3}

and a hole concentration of

5 \times 10^{12} {cm}^{- 3}

. The semiconductor is

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What type of impurity is added to obtain

n

-type semiconductor?

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A semiconductor has the electron concentration of

8 \times 10^{13} c m^{- 3}

and hole concentration of

4 \times 10^{13} c m^{- 3} .

Is the semiconductor p-type or n-type? Also, calculate the resistivity of this semiconductor. Given electron mobility

= 24,000 c m^{2} V^{- 1} s^{- 1}

and hole mobility

= 200 c m^{2} V^{- 1} s^{- 1}

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Why are elemental dopants for Silicon or Germanium usually chosen from group

XIII

or group

XV

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Suppose a

‘ n ’

-type wafer is created by doping

Si

crystal having

5 \times 10^{28} atoms / m^{3}

with

1 ppm

concentration of

A s

. On the surface

200 ppm

Boron is added to create

‘ P ’

region in this wafer.Considering

n_{i} = 1.5 \times 10^{16} m^{- 3}

, (i) Calculate the densities of the charge carriers in the

n & p

regions. (ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.

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Pure silicon at

300 K

has equal electron and hole concentrations of

1.5 \times 10^{16} m^{- 3} .

Doping by indium increases the hole concentration to

4.5 \times 10^{22} m^{- 3} .

Calculate the new electron concentration in the doped silicon.

Which of the following industries is based on the input or raw material of iron ore?

Important Questions on Electromagnetic Induction

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