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प्रश्न
Describe the two main types of semiconductors and contrast their conduction mechanism.
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उत्तर
The two main types of semiconductors are:
- n-type semiconductor
- p-type semiconductor
(1) n-type semiconductor:
- The semiconductor whose increased conductivity is a result of negatively charged electrons is called an n-type semiconductor.
- When the crystal of a group 14 element like Si (Silicon) or Ge (Germanium) is doped with a group 15 element like P (Phosphorus) or As (Arsenic), an n-type semiconductor is formed.
- Si and Ge each have four valence electrons.
- In their crystals, each Si or Ge atom forms four covalent bonds.
- P and As contain five valence electrons each.
- When Si or Ge is doped with P or As, these elements take up some of the crystal’s lattice sites.
- Four out of five electrons from P, or As, are used in the formation of covalent bonds with four neighbouring Si or Ge atoms.
- The remaining fifth electron is delocalised, which increases the conductivity of the doped Si or Ge.
(2) p-type semiconductor:
- The semiconductor whose increase in conductivity is a result of an electron hole is called a p-type semiconductor.
- When a crystal of group 14 elements such as Si (Silicon) or Ge (Germanium) is doped with a group 13 element such as B (Boron), Al (Aluminum), or Ga (Gallium) (which contain only three valence electrons), a p-type semiconductor is formed.
- When a Si crystal is doped with B, the three valence electrons are used to form three covalent bonds with neighbouring Si atoms.
- The fourth bond needed to complete the Si’s covalent bonding is missing, creating an electron hole in the lattice.
- An electron from a neighbouring atom can move and fill the electron hole. However, in doing so, it creates an electron hole at its original position.
- This process makes it seem like the electron hole is moving opposite the electron that filled it.
- When an electric field is applied, electrons move toward the positively charged plate through the electron holes.
- It will appear as if the electron holes are positively charged and are moving toward the negatively charged plate.
संबंधित प्रश्न
A group 14 element is to be converted into n-type semiconductor by doping it with a suitable impurity. To which group should this impurity belong?
What is a semiconductor?
Non-stoichiometric cuprous oxide, Cu2O can be prepared in laboratory. In this oxide, copper to oxygen ratio is slightly less than 2 : 1. Can you account for the fact that this substance is a p-type semiconductor?
Classify each of the following as being either a p-type or a n-type semiconductor:
- Ge doped with In
- B doped with Si
Explain the following with suitable examples:
12-16 group compounds
What type of semiconductor is obtained when
Si is doped with P?
Solids with conductivities ranging from 104 to 107 ohm-1 m-1 are ____________.
Semiconductors have conductivity (in ohm-1 m-1) in the range of ____________.
The process by which impurity is introduced in semiconductors to enhance its conductivity is known as ____________.
Electrical conductivity of semiconductors increases with increase in ____________.
Silicon doped with electron-rich impurity forms ______.
Which of the following statements are true about semiconductors?
(i) Silicon doped with electron-rich impurity is a p-type semiconductor.
(ii) Silicon doped with an electron-rich impurity is an n-type semiconductor.
(iii) Delocalised electrons increase the conductivity of doped silicon.
(iv) An electron vacancy increases the conductivity of n-type semiconductor.
Why are solids incompressible?
Why does the electrical conductivity of semiconductors increase with rise in temperature?
Silicon is a/an ______
