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प्रश्न
How does the doping increase the conductivity of semiconductors?
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उत्तर
For pratical use conductivity of a semiconductor is very low conductivity can be increased by adding small impurity, this process is called doping. Doping can be done with an impurity which ie electron rich or electron deficient.
• n-type semiconductors: Silicion or Germanium (group - 14) doped with electron rich impurity (group - 15 element like P or As) is called n-tyoe semiconductors. Here conductivity is due to the extra electron or delocalized electron.
Explanation for increase in conductivity in n-type semiconductors: When intrinsic semiconductors like Si or Ge are doped with pentavalent elements as P or As, they occupy some of the lattice sites in silicon or germanium crystal. Four out of five electrons are used in formation of four covalent bonds with neighbouring silicion atoms. The fifth electron is extra and gets delocalised. These delocalised electrons increase the conductivity of doped silicion (or germainium)
• p-type semiconductors: Silicion or Germanium (group - 14) doped with electron deficient impurity (group 13 element like B or Al or Ga) is called p-type semiconductors. HEre conductivity is due to positively charged electron holes.
Explanation for increase in conductivity in p-type semiconductors: In this case the doping of intrinsic semiconductors like silicion or germanium with trivalent elements like B/In/Ga, three out of four electrons in silicion or germanium form bonds with doping impurity (i.e. B/In/Ga). The fourth electron remains unbonded. The place where fourth valence electron is missing is called electron hole or electron vacancy. An electron from neighbouring atom can come and fill up the lectron hole, but in doing so it would leave an electron hole at its original position. If this happens it would appear that electron hole has moved in a direction opposite to that of the electron that filled it. Under the influence of electric field electrons would move towards the positively charged plate through electron holes, but it would appear as if electrons are positively charged and are moving towards the negatively charged plate.
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संबंधित प्रश्न
p - type semi-conductors are made by mixing silicon with impurities of ______.
In a semiconductor, acceptor impurity is.................................
- antimony
- indium
- phosphorous
- arsenic
What type of semiconductor is obtained when silicon is doped with boron?
To prepare n-type semiconductor the impurity to be added to silicon should have the following number of valence electrons:
(a) 2
(b) 3
(c) 4
(d) 5
Give reasons : Silicon on doping with Phosphorous forms n-type semiconductor.
A pure semiconductor is ________.
(a) an extrinsic semiconductor
(b) an intrinsic semiconductor
(c) p-type semiconductor
(d) n-type semiconductor
Distinguish between p-type and n-type semiconductors.
What is the ratio of octahedral holes to the number of anions in hexagonal closed packed structure?
A group of 14 elements is converted into n-type semiconductor by doping it with:
In n-type semiconductor, current is carried by ____________.
Which transition metal oxide has appearance and conductivity like that of copper?
To get n-type of semiconductor, germanium should be doped with ____________.
p-type semiconductors are formed when Si or Ge are doped with ____________.
Which of the following oxides behaves as conductor or insulator depending upon temperature?
To get a n-type semiconductor from silicon, it should be doped with a substance with valence ______.
A perfect crystal of silicon (Figure) is doped with some elements as given in the options. Which of these options show n-type semiconductors?
