mcqs on n type semiconductor

mcqs on n type semiconductor

1. Which of the following doping elements would not be suitable for converting intrinsic semiconductor to n-type

  • A.Phosphorous
  • B.Indium
  • C.Antimony
  • D.Arsenic

2. As the temperature of a semiconductor increases its

  • A.Conductivity increases
  • B.Resistivity increases
  • C.Atomic number decreases
  • D.Temperature co-efficient becomes zero

3. In a n-type semiconductor, the positive of the Fermi level

  • A.Is at the centre of the energy gap
  • B.Is lower than the centre of energy gap
  • C.Is higher than the centre of energy gap
  • D.Can be anywhere depending upon the doping concentration

4. Which of the following cannot exist outside a semiconductor

  •  A.Hole
  •  B.Electron
  •  C.Both (a) and (b)
  •  D.None of the above

5. In semiconductor the forbidden energy gap lies

  • A.Just below the conduction band
  • B.Just above the conduction band
  • C.Either above or below the conduction band
  • D.Between the valence band and conduction band

6. An n-type semiconductor is formed by ……… bonds.

  • A.Covalent
  • B.Electrovalent
  • C.Co-ordinate
  • D.None of the above

7. An n-type semiconductor is

  • A.Positively charged
  • B.Negatively charged
  • C.Electrically neutral
  • D.None of the above

8. The strength of a semiconductor crystal comes from

  • A.Forces between nuclei
  • B.Forces between protons
  • C.Electron-pair bonds
  • D.None of the above

9. The impurity level in an extrinsic semiconductor is about of pure semiconductor.

  • A.10 atoms for 108 atoms
  • B.1 atom for 108 atoms
  • C.1 atom for 104 atoms
  • D.1 atom for 100 atoms

10. A hole and electron in close proximity would tend to

  • A.Repel each other
  • B.Attract each other
  • C.Have no effect on each other
  • D.None of the above

11. n-type semiconductor is obtained by doping silicon with ……..

  • A.phosphorus
  • B.Aluminium
  • C.germanium
  • D.boron

12. What is produced by doping of silicon with arsenic

  • A.n-type
  • B.conductor
  • C.insulator
  • D.p type

13. In n-type semiconductors majority charge carriers are

  • A.holes
  • B.electrons
  • C.neon
  • D.all of above

14. The donor impurity must have …. electrons.

  • A. 3
  • B. 4
  • C. 5
  • D. 6

15. n-type semiconductors are …… semiconductors.

  • A.intrinsic
  • B.extrinsic
  • C.pure
  • D.none of above

n-type semiconductors

“When a small amount of pentavalent impurity is added to a pure semiconductor , which provide a large number of free electrons in it, the extrinsic semiconductor thus formed is known as n-type semiconductor”.

Let us consider what happen if a small amount of pentavalent impurity, for example  phosphorus is added to a sample of intrinsic germanium .

Phosphorus atom has 5 Valence electrons, four of these form covalent bonds with neighbouring germanium atom. The fifth electron has no chance of forming a covalent bond. Since it is not associated with any covalent bond ,also it is quite far from the nucleus and it is very loosely bound.

It requires very little energy from the attractive force of its nucleus (0.01 electron volt in case of Germanium and 0.05 electron volt in case of silicon). This energy is so small that at room temperature practically all such electrons become free.

Or we can say at room temperature ,each impurity atom donates one free electron to the conduction band ,this is the reason why this impurity is called donor type.


Donor impurity


In other words, Such impurities which provide n-type semiconductor i.e. pentavalent impurity also known as Donor impurity, because each atom of them donate one free electron to the semiconductor crystal. Addition of pentavalent impurity provides a large number of free electrons in the semiconductor system.

Arsenic , Antimony (having atomic number 33 ,51 resp.), provide a large number of free electrons in the semiconductor crystal .

When a small amount of pentavalent impurity like arsenic , atomic number 33 electronic configuration (2 8  18  5)  having 5 valence electrons is added to Germanium crystal, each atom of the impurity fits in the Germanium crystal in such a way that its four electrons form covalent bond with four Germanium atoms

where as the fifth electron finds no place in the covalent bonds and is thus free .Hence each arsenic atom provides one free electrons in the Germanium crystal .

Since an extremely small amount of arsenic impurity has a large number of atoms, therefore it provides millions of free electrons for conduction .

With the addition of pentavalent impurity a large number of free electrons are made available in the conduction band these electrons are the free electrons which did not fit in the covalent bond of the Crystal (i.e. fifth electron of each arsenic atom) .

However a minute quantity of free electrons are also available in the conduction band which are produced when thermal energy at room temperature is a imparted to the Germanium crystal forming hole electron pair .

So a large number of free electrons are made available by the addition of pentavalent impurity.
A minute quantity of free electrons are made available by the generation of electron pair when thermal energy at room temperature is imparted to the semiconductor crystal, these electrons leaves behind holes in the valence band .

Conduction through n-type semiconductor

In n-type semiconductor a large number of free electrons (donated by the impurity atoms) are available in the conduction band .When a potential difference is applied across this type of semiconductor, the free electrons are directed towards the positive terminal constituting electric current.

As the flow of current through the Crystal is constituted by free electrons which are carriers of negative charge, therefore this type of conductivity is called negative Or n-type conductivity.

It may be noted that conduction through n-type semiconductor is similar to that of conduction through metal like Copper. It is seen that at room temperature ,electron-hole pair are formed.

These holes which are available in minute quantity in valance band also constitutes a little current in a semiconductor. So this about n-type semiconductor.

mcqs on n type

mcqs on n type semiconductor

 mcqs on n type semiconductor
Electronics MCQs

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