Tag: impurity defects

Questions Related to impurity defects

Doping of $As$ with $Si$ is called :

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. n-type semi-condutor

  2. p-type semi-conductor

  3. intrinsic semi-conductor

  4. None of the above

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Correct Option: A
Explanation:

$As$ is a member of group $V$ and has 5 electrons in its outermost shell. 


When $Si$ is doped with group $V$ elements such as $As$ then, $Si$ forms four bonds with $As$ and one extra electron is left free for conduction. 

Since the conduction is due to the presence of free electrons, therefore, it is known as n-type semiconductor.

Therefore, the option is A.

An n-type semi-conductor is formed when a trace amount of impurity is added to silicon. The number of valence electrons in the impurity atom must be: 

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $3$

  2. $5$

  3. $1$

  4. $2$

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Correct Option: A
Explanation:

An n-type semiconductor is due to the presence of a free electron in the semiconductor. Since silicon is an element having $4$ valence electrons, in order to have a free electron, it must be doped with an element having one more valence electron than silicon. 


Hence the number of valence electron in the impurity must be $4+1=5.$

Therefore, option B is correct.

Which of the following statements is correct about the conduction of electricity in pure crystal of silicon at room temperature?

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. The conduction is due to electrons present in fully occupied lowest energy states.

  2. The conduction is due to only some electrons capable of leaving the bonds at room temperature.

  3. The conduction is only due to the holes formed from the release of electrons.

  4. The conduction is due to the movement of both the electrons released and holes formed.

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Correct Option: D
Explanation:

In semiconductor two types of the semiconductor are present. They are an intrinsic and extrinsic semiconductor. A pure silicon crystal is an example of an intrinsic semiconductor. 

The conduction in the intrinsic semiconductor is due to the moving of electrons from valence bond to conduction bond by means of thermal energy. Due to the thermal energy the $Si-Si$ bond breaks and creates electron deficiency which is also called a hole. So, both the holes and electrons released to account for the conduction of electricity.

p type semi conductor is formed when trace amount of impurity is added to silicon. The number of valence electrons in the impurity atom must be:

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $3$

  2. $5$

  3. $1$

  4. $2$

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Correct Option: A
Explanation:

To form a p-type semiconductor, one must add elements from boron family to the silicon atom.

Boron family has 3 valance electrons so, number of valance electrons in the impurity atom must be 3.

Solar cell is constructed by connecting the semi conductors of_____________

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. n-type and n-tupe

  2. n-type and p-type

  3. p-type and p-type

  4. n-type and n-pn-type

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Correct Option: A

A semiconductor obtained by doping silicon with elements of group 13 and group is respectively is

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. P - type

  2. n - type

  3. p type, n type

  4. n type, p type.

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Correct Option: A

Which of the following acts as a superconductor at $4K$?

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $He$

  2. $Cu$

  3. $K$

  4. $Mg$

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Correct Option: A

Addition of arsenic in small amount to pure germanium will result in the formation of

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. n-type semiconductor

  2. germanium arsenide

  3. p-type semiconductor

  4. a superconducting alloy

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Correct Option: A

To get n-type doped semiconductor, impurity to be added to silicon should have number of valence electrons equal to: 

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $1$

  2. $2$

  3. $3$

  4. $5$

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Correct Option: D
Explanation:

To get n-type doped semiconductor, pentavalent impurity should be added to silicon. Example- As in Si.

A solid with high electrical and thermal conductivity is:

chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. $Si$

  2. $Li$

  3. $NaCl$

  4. $Ice$

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Correct Option: B